Global Surface Air Temperatures

[AbruptSLR]

Increasing climate sensitivity from 3 to 4.5, and naively upscaling CMIP 5 model runs by 50% suggests that the current global temperature should be about 1.5 C above the 1950-80 baseline.  Even with a monster el nino and a massive temp spike that has quite surprised many (me included) we are still not that high.

I would be very surprised if temperatures do not drop in the next year or two back towards the long term trend.  The CMIP5 model projection for 2016 is 0.96 degrees above the 1950-80 baseline.  Tamino suggests that GISS can vary by almost +/- 0.4 degree either side of his trend line.  The GISS measured 1.33 degrees is close to the upper range of what we would expect to see for trend + random noise, and certainly not obviously outside this range.

First (In addition to Sherwood (2014)], the linked Thompson (2015) reference indicates that ECS has a 95%CL range of from 3C to 6.3C, with a best estimate of 4C:

Climate sensitivity by Roy Thompson published by Earth and Environmental Science Transactions of the Royal Society of Edinburgh, DOI: 10.1017/S1755691015000213

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10061758&fileId=S1755691015000213

Second, the following linked article reminds us that we are now in a positive PDO phase, and we are likely to have faster than typical increases in GMST through 2030

http://www.climatecentral.org/news/earth-experiences-global-warming-spurt-19877

Extract: "The effects of the PDO on global warming can be likened to a staircase, with warming leveling off for periods, typically of more than a decade, and then bursting upward.
“It seems to me quite likely that we have taken the next step up to a new level,” said Kevin Trenberth, a scientist with the National Center for Atmospheric Research.
The 2014 flip from the cool PDO phase to the warm phase, which vaguely resembles a long and drawn out El Niño event, contributed to record-breaking surface temperatures across the planet in 2014.
The record warmth set in 2014 was surpassed again in 2015, when global temperatures surged to 1°C (1.8°F) above pre-industrial averages, worsening flooding, heatwaves and storms.
…
“Last time we went from a negative to a positive was in the mid-‘70s,” said Gerald Meehl, a National Center for Atmospheric Research scientist. “Then we had larger rates of global warming from the ‘70s to the late ‘90s, compared to the previous 30 years.”
“It’s not just an upward sloping line,” Meehl said. “Sometimes it’s steeper, sometimes it’s slower.”"

[BornFromTheVoid]

At +1.35C above the 51-80 average, the GISS temperature for February was warmest on record by +0.47C.



The 12 month rolling average is now at +0.93C

[AbruptSLR]

Joe Romm makes several good points about the current peak in GISS temperatures (see the linked article).  The first images both shows and discusses the fact that the GISS Temp has peaked for each the previous five months, while the second image (from Hotwhopper) shows that while the 1997-98 El Nino had a sharp peak in February 1998 (pointed out by Nick Stokes); the 2015-16 El Nino has a broad left shoulder going up, which raises the question of whether it might also have a broad right shoulder going down.

http://thinkprogress.org/climate/2016/03/13/3759569/record-february-warmth-alaska-arctic/

[Steven]

As 2030 is a little way into the future; do you believe that a 1.2C value at the end of 2016 is plausible?

Currently it seems likely that 2016 will be more than 0.1°C warmer than 2015, in terms of annual average global temperature.  For the GISS dataset that would imply a 2016 annual average of about 1.2°C (or slightly more) above the late 19th century 1880-1899 average. 

The corresponding value for Michael Mann's graph upthread could be as high as 1.4°C or 1.5°C or so, but as mentioned, Mann is using only Northern Hemisphere data.

Anyway, I am more interested in ENSO-corrected temperature.  For 2015, the El Nino contribution to the annual mean global temperature was probably somewhere between 0.05°C and 0.1°C, depending on what methodology is used.  For 2016, the El Nino contribution could be about 0.2°C or so.  Tamino's graph below suggests that an ENSO-contribution of that magnitude happened in the previous Super El Nino years 1998 and 1983:



https://tamino.wordpress.com/2016/01/27/el-nino-and-the-2015-record-breaking-heat/

[AbruptSLR]

Anyway, I am more interested in ENSO-corrected temperature.  For 2015, the El Nino contribution to the annual mean global temperature was probably somewhere between 0.05°C and 0.1°C, depending on what methodology is used.  For 2016, the El Nino contribution could be about 0.2°C or so.  Tamino's graph below suggests that an ENSO-contribution of that magnitude happened in the previous Super El Nino years 1998 and 1983:

For what little it is worth, you may wish to consider developing corrections/adjustments not only for ENSO events, but also for PDO/IPO events (or possibly other multi-decadal cycles).

[Michael Hauber]

First (In addition to Sherwood (2014)], the linked Thompson (2015) reference indicates that ECS has a 95%CL range of from 3C to 6.3C, with a best estimate of 4C:

Climate sensitivity by Roy Thompson published by Earth and Environmental Science Transactions of the Royal Society of Edinburgh, DOI: 10.1017/S1755691015000213

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10061758&fileId=S1755691015000213

Have you read that paper?  It is very silly. 

They do a correlation model with the four factors GHG, aerosol, ENSO and volcano.  There is no allowance for time lags due to thermal inertia, so what they are really trying to calculate is transient sensitivity and not equilibrium sensitivity.  The only possible way they can get such a high GHG sensitivity is by allowing aerosol forcing to have an even higher sensitivity.  Consider that their model would calculate a warming due to GHG of about 3 degrees has already occurred.  Their model would also imply an equilbrium sensitivity much higher than 4 degrees (assuming that equilibrium sensitivity is higher than transit).

Second, the following linked article reminds us that we are now in a positive PDO phase, and we are likely to have faster than typical increases in GMST through 2030

http://www.climatecentral.org/news/earth-experiences-global-warming-spurt-19877

Tamino finds that there is no statistically significant change in trend between 1970 and now, despite the fact that we had a positive phase from 1976 to 1998 (or 2007) and a negative phase after that.  From my analysis of shorter term trend variations the effect seems to be almost entirely based on changing the frequency of warm el nino years vs cool La Nina years.  We are in a very warm el nino year, and there will be further warming due to +ve PDO.  The next warm el nino year will not jump any further ahead of the current year than it would in a -ve PDO.  But what we will see if the +ve PDO continues is less cool La Nina years in the next decade, meaning that a trend from say 2000 to 2025 will be steeper than it would be if it was held back by a larger number of cool La Nina years during a -ve PDO.

[AbruptSLR]

First (In addition to Sherwood (2014)], the linked Thompson (2015) reference indicates that ECS has a 95%CL range of from 3C to 6.3C, with a best estimate of 4C:

Climate sensitivity by Roy Thompson published by Earth and Environmental Science Transactions of the Royal Society of Edinburgh, DOI: 10.1017/S1755691015000213

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10061758&fileId=S1755691015000213

Have you read that paper?  It is very silly. 

They do a correlation model with the four factors GHG, aerosol, ENSO and volcano.  There is no allowance for time lags due to thermal inertia, so what they are really trying to calculate is transient sensitivity and not equilibrium sensitivity.  The only possible way they can get such a high GHG sensitivity is by allowing aerosol forcing to have an even higher sensitivity.  Consider that their model would calculate a warming due to GHG of about 3 degrees has already occurred.  Their model would also imply an equilbrium sensitivity much higher than 4 degrees (assuming that equilibrium sensitivity is higher than transit).

Second, the following linked article reminds us that we are now in a positive PDO phase, and we are likely to have faster than typical increases in GMST through 2030

http://www.climatecentral.org/news/earth-experiences-global-warming-spurt-19877

Tamino finds that there is no statistically significant change in trend between 1970 and now, despite the fact that we had a positive phase from 1976 to 1998 (or 2007) and a negative phase after that.  From my analysis of shorter term trend variations the effect seems to be almost entirely based on changing the frequency of warm el nino years vs cool La Nina years.  We are in a very warm el nino year, and there will be further warming due to +ve PDO.  The next warm el nino year will not jump any further ahead of the current year than it would in a -ve PDO.  But what we will see if the +ve PDO continues is less cool La Nina years in the next decade, meaning that a trend from say 2000 to 2025 will be steeper than it would be if it was held back by a larger number of cool La Nina years during a -ve PDO.

It is my understanding that the Thompson (2015) reference was kept relatively simple so that it would be suitable for presentation at the CoP21 in Paris.  Nevertheless, its conclusions essentially match the more sophisticated paper by Tian (2015) that indicates that the double-ITCZ bias constrains ECS to its high end (around 4.0C):

Tian, B. (2015), "Spread of model climate sensitivity linked to double-Intertropical Convergence Zone bias", Geophys. Res. Lett., 42, doi:10.1002/2015GL064119.

Regarding the PDO, yes it does decrease the frequency of La Nina events; and the likelihood of a La Nina event occurring later this year has been decreasing steadily this entire year (see the 2015-16 El Nino thread); which might well leave 2016 much warmer than your, or Tamino's, linear trend-lines indicate.

[AbruptSLR]

The Washington Post offers the linked article about the Feb 2016 GMST spike, and the offer the attached image of NASA surface temp anoms (referenced to a 1951-1980 baseline), sub-divided between Meteorological Stations and Land-Ocean Temperature Index data through Feb 2016:

https://www.washingtonpost.com/news/capital-weather-gang/wp/2016/03/14/the-planet-had-its-biggest-temperature-spike-in-modern-history-in-february/

[Michael Hauber]

  Nevertheless, its conclusions essentially match the more sophisticated paper by Tian (2015) that indicates that the double-ITCZ bias constrains ECS to its high end (around 4.0C):

Tian, B. (2015), "Spread of model climate sensitivity linked to double-Intertropical Convergence Zone bias", Geophys. Res. Lett., 42, doi:10.1002/2015GL064119.

The operative word from that study is that the sensitivity might be in the high end.  Models that represent various cloud and tropical processes seem to have a higher sensitivity.  But models that represent historical global temperatures have a moderate sensitivity.

And what if sensitivity is at the high end?  Out of CMIP5 the second highest climate sensitivity is HADGEM2-ES with a sensitivity of 4.59.  The temperature projection for this model suggests a 2016 temp of 1.11 above baseline, compared to 0. 96 for all models, and for 2100 under scenario 8.5 a temp of 5.47, compared to 4.56 for all models.

The projected warming for high sensitivity models is not nearly as high as you get by scaling the projection according to sensitivity (e.g. 4.5 high sensitivity/3 avg sensitivity * 4.5 temp in 2100 = 6.8 temp in 2100).  The models can only warm things up over decades to century or two time frames just a little bit faster than the model average, otherwise the gap between model and observed temperature history becomes very large.

[AbruptSLR]

  Nevertheless, its conclusions essentially match the more sophisticated paper by Tian (2015) that indicates that the double-ITCZ bias constrains ECS to its high end (around 4.0C):

Tian, B. (2015), "Spread of model climate sensitivity linked to double-Intertropical Convergence Zone bias", Geophys. Res. Lett., 42, doi:10.1002/2015GL064119.

The operative word from that study is that the sensitivity might be in the high end.  Models that represent various cloud and tropical processes seem to have a higher sensitivity.  But models that represent historical global temperatures have a moderate sensitivity.

And what if sensitivity is at the high end?  Out of CMIP5 the second highest climate sensitivity is HADGEM2-ES with a sensitivity of 4.59.  The temperature projection for this model suggests a 2016 temp of 1.11 above baseline, compared to 0. 96 for all models, and for 2100 under scenario 8.5 a temp of 5.47, compared to 4.56 for all models.

The projected warming for high sensitivity models is not nearly as high as you get by scaling the projection according to sensitivity (e.g. 4.5 high sensitivity/3 avg sensitivity * 4.5 temp in 2100 = 6.8 temp in 2100).  The models can only warm things up over decades to century or two time frames just a little bit faster than the model average, otherwise the gap between model and observed temperature history becomes very large.

MH,

I have to begin by stating that I admire your (& Steven's) command of this topic; and I freely admit that there are ranges on all of the pertinent values in this discussion; including that the Tian (2015) only states that “... ECS might be in the higher end of its range (~4.0^oC) ...”.

That said, we started this line of discussion when I stated that exceeding the 2C limit was plausible by 2030, and in this line the linked Kevin Anderson article notes that to avoid the 2C limit our remaining CO2 budget might be about 450 Gt; however, this ignores the risks that climate sensitivity may well be higher than assumed by AR5:

http://www.skepticalscience.com/Anderson.html

Extract: "Therefore, instead of a 1000 Gt CO2 budget, we might only have 450 Gt available for fossil-fuel energy emissions.”

I note that we are currently emitting more than 53Gt of CO2-e a year (see attached image), so Anderson is indicating that we might only have 8.5 more years (pulse an effective lag time of say 5.5 to 7.5 years for the emission period from 2016 to 2030) until 2030 to 2032 when we exceed the 2C limit (assuming an AR5 climate sensitivity, and assuming a GWP100 for methane of 34, while GWP20 for methane is 105). Furthermore, I note that about 1.75 years ago we were at about 0.85C above pre-industrial levels and now we are above 1.1C, and Steven thinks that we could reach 1.2C above pre-industrial by the end of this year.


Also, while the linked (open access) reference has many appropriate qualifying statements and disclaimers, it notes that the AR5 paleo estimates of ECS were linear approximations that change when non-linear issues are considered.  In particular they find for the specific ECS, S[CO2,LI], during the Pleistocence (ie the most recent 2 million years) that:

"During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions."

Therefore, researchers such as James Hansen who relied on paleo findings that during recent full glacial periods ECS was about 3.0C, did not know that during interglacial periods this value would be 45% larger, or 4.35C.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.


http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf

Furthermore, the linked Knutti & Rogenstein (2015) open access reference addresses the limits of linear climate models (w.r.t. accessing climate sensitivity) and states: "But all comprehensive climate models indicate sensitivities above 2°C, and those that simulate the present-day climate best even point to a best estimate of ECS in the range of 3–4.5°C."


Reto Knutti, Maria A. A. Rugenstein (2015), "Feedbacks, climate sensitivity and the limits of linear models", Philosophical Transactions of the Royal Society A, DOI: 10.1098/rsta.2015.0146

http://rsta.royalsocietypublishing.org/content/373/2054/20150146


Also, the linked Bloch-Johnson, Pierrehumbert & Abbot (2015) reference assumes different degrees of nonlinearity for climate feedback mechanisms and concludes that such nonlinearity for positive feedback represents a Black Swan risk that linear climate models cannot recognize:

Jonah Bloch-Johnson, Raymond T. Pierrehumbert & Dorian S. Abbot (24 June 2015), "Feedback temperature dependence determines the risk of high warming", Geophysical Research Letters, DOI: 10.1002/2015GL064240

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064240/full

Finally, w.r.t. Black Swan risks I note that there are numerous factors that could have recently masked the impacts of relatively high ECS values including: (a) more negative anthropogenic & natural aerosol forcing & feedbacks than previously assumed, (b) poor understanding of Earth System states (like the PDO phase, etc), (c) the recent [but temporary] surge in plant growth related to our high CO2 concentrations. and (d) certain nonlinear positive feedbacks may be now accelerating due to global warming.

Best,
ASLR

[AbruptSLR]

To those keeping track of my various posts, my last post Reply #863 may seem Pollyannaish (i.e. ESLD) for reasons including:
(a) I assumed a CO₂-e value of 53 Gt over the period from 2016 to 2030; which assumes that the Paris Pact (CoP21) is 100% effective, and uses only the 50% CL level for emissions (while a 95%CL for RCP 8.5 may be more appropriate for risk evaluation); while the linked Washington Post article (and the two cited studies) seriously question whether the Paris Pact emission targets can be achieved; and
(b) I did not emphasize that an El Nino skewed (due to warming) ENSO cycle can result in non-linear acceleration of numerous positive feedback mechanisms including: accelerated carbon emissions from tropical rainforests during droughts (El Nino periods); accelerated methane emissions from tropical rainforests during flood periods (La Nina periods); Arctic Amplification (due to accelerated telecommunication of heat & water vapor to the Arctic); and increase tropical and boreal forest fires.

https://www.washingtonpost.com/news/energy-environment/wp/2016/03/15/temperatures-are-spiking-can-we-keep-global-warming-in-the-safe-range/

Extract: "…. two pieces of new research have questioned whether, from an energy standpoint, keeping long term warming below 2 degrees C is even likely to be possible."


Richard G. Newell, Yifei Qian, Daniel Raimi (March 2016), "Global Energy Outlook 2015", National Bureau of Economic Research, NBER Working Paper No. 22075


http://nber.org/papers/w22075

Abstract: "This paper assesses trends in the global energy sector through 2040 by harmonizing multiple projections issued by private, government, and inter-governmental organizations based on methods from “Global Energy Outlooks Comparison: Methods and Challenges” (Newell and Qian 2015). These projections agree that global energy consumption growth in the coming 25 years is likely to be substantial, with the global demand center shifting from Europe and North America to Asia, led by China and India. Most projections show energy demand growing as much or more in absolute terms to 2040 than previous multi-decade periods, although the rate of growth will be slower in percentage terms. Total consumption of fossil fuels grows under most projections, with natural gas gaining market share relative to coal and oil. The North American unconventional gas surge has expanded to tight oil more rapidly than anticipated, with implications for global oil markets that are still unfolding. Renewable electricity sources are also set to expand rapidly, while the prospects for nuclear power are more regionally varied. Global carbon dioxide emissions continue to rise under most projections and, unless additional climate policies are adopted, are more consistent with an expected rise in average global temperature of close to 3°C or more, than international goals of 2°C or less."

Glenn A. Jones & Kevin J. Warner (June 2016), "The 21st century population-energy-climate nexus
Energy Policy, Volume 93, Pages 206–212, doi:10.1016/j.enpol.2016.02.044


http://www.sciencedirect.com/science/article/pii/S0301421516300830


Abstract: "World population is projected to reach 10.9 billion by 2100, yet nearly one-fifth of the world's current 7.2 billion live without access to electricity. Though universal energy access is desirable, a significant reduction in fossil fuel usage is required before mid-century if global warming is to be limited to <2 °C. Here we quantify the changes in the global energy mix necessary to address population and climate change under two energy-use scenarios, finding that renewable energy production (9% in 2014) must comprise 87–94% of global energy consumption by 2100. Our study suggests >50% renewable energy needs to occur by 2028 in a <2 °C warming scenario, but not until 2054 in an unconstrained energy use scenario. Given the required rate and magnitude of this transition to renewable energy, it is unlikely that the <2 °C goal can be met. Focus should be placed on expanding renewable energy as quickly as possible in order to limit warming to 2.5–3 °C."

[AbruptSLR]

The linked SkS article not only discusses their 2C Track plot (previously in Reply #837) but goes on to speculate on the rest of 2016 by offering the attached extrapolated image and the following extract.  I must reiterate that the 2015-16 El Nino has been more uniform (less peaky) than the 1997-98 El Nino; and that a La Nina occurred in late 1998, which is looking less and less likely to occur in late 2016; so the attached SkS plot probably errs on the side of least drama (ESLD):

https://www.skepticalscience.com/2c-2016-02.html

Extract: "Of course, everyone likely knows by now that the big news of late has been the v4 update to the RSS satellite data set, which raised the trend in their data by about 60%. Currently I've been working with the lower troposphere data (TLT) and the RSS update so far is only for the TMT and TTT data. I haven't heard otherwise, but I'm assuming an update for TLT will also be coming.
Given that February was such a huge jump relative to January in the GISS data and the surface station data seems to lead the satellite data in response to El Ninos, I think we're likely in for at least a few more very interesting months. This phase of the temperature trend is probably going to continue on at least through the NH summer and into the NH fall.
Buckle your seat belts. This is where the ride starts getting interesting."

[AbruptSLR]

The link leads to a guest post by Tamino at SkS and summarizes a wide range of graphs showing fluctuations superimposed on upward trends for GMST, SLR, ASIE, CO2 concentrations, etc.  While it is a nice summary his conclusions indicate how good people & scientists spend so much effort defending against crack-pot denialist theories that they do not spend enough effort on projection nonlinear accelerations in those upward trend lines.

https://www.skepticalscience.com/gw-basics-what-has-changed.html

[BornFromTheVoid]

May record smashed on the latest SOTC report.
http://www.ncdc.noaa.gov/sotc/summary-info/global/201602

Global highlights: February 2016

• The February average temperature across global land and ocean surfaces was 2.18°F (1.21°C) above the 20th century average. This was not only the highest for February in the 1880–2016 record (surpassing the previous record set in 2015 by 0.59°F / 0.33°C), but it surpassed the all-time monthly record set just two months ago in December 2015 by 0.16°F (0.09°C). February 2016 also marks the 10th consecutive month a monthly global temperature record has been broken.
  
  
• The February globally-averaged land surface temperature was 4.16°F (2.31°C) above the 20thcentury average. This was the highest for February in the 1880–2016 record, surpassing the previous records set in 1998 and 2015 by 1.13°F (0.63°C) and surpassing the all-time single-month record set in March 2008 by 0.77°F (0.43°C).
  
  
• The February globally-averaged sea surface temperature was 1.46°F (0.81°C) above the 20thcentury average. This was the highest for February in the 1880–2016 record, surpassing the previous record set in 2010 by 0.36°F (0.20°C) , and was the sixth highest departure from average among all 1,646 months in the record. The nine highest monthly global ocean temperature departures have all occurred in the past nine months (since July 2015).
  
  
• The February temperature for the lower troposphere (roughly the lowest 5 miles of the atmosphere) was the highest in the 1979–2016 record, at 1.62°F (0.90°C) above the 1981–2010 average, as analyzed by the University of Alabama in Huntsville (UAH) using version 5.6. It was also highest on record, at 1.57°F (0.87°C) above the 1981–2010 average, as analyzed by Remote Sensing Systems (RSS). The February 2016 departures from average are also the highest for any month in the 38-year period of record, surpassing the previous record set in April 1998 by 0.43°F (0.24°C) for UAH and by 0.23°F (0.13°C) for RSS.
  
  
• The February temperature for the mid-troposphere (roughly 2 miles to 6 miles above the surface) was the highest for this month in the 1979–2016 record, at 1.31°F (0.73°C) above the 1981–2010 average, as analyzed by UAH. It was also highest on record, at 1.33°F (0.74°C) above the 1981–2010 average, as analyzed by RSS. After removing the influence of temperatures above 6 miles in altitude, the University of Washington, using data analyzed by the UAH and RSS, calculated temperature departures from the 1981–2010 average to be 1.60°F (0.89°C) and 1.57°F (0.87°C), respectively, both highest in the record. The February 2016 departures from average are also the highest for any month in the 38-year period of record, surpassing the previous record set in April 1998 by 0.13°F (0.07°C) for UAH and by 0.09°F (0.05°C) for RSS.
  
  
• The average Arctic sea ice extent for February was 450,000 square miles (7.54 percent) below the 1981–2010 average. This was the smallest February extent since records began in 1979 and 77,000 square miles smaller than the previous record of 2005. February 2016 also marked the second consecutive month of record low Arctic sea ice extent, according to analysis by the National Snow and Ice Data Center based on data from NOAA and NASA.
  
  
• Antarctic sea ice during February was 110,000 square miles (9.54 percent) below the 1981–2010 average. This was the sixth smallest Antarctic sea ice extent for February in the 38-year period of record and the smallest since 2011.
  
  
• According to data from NOAA analyzed by the Rutgers Global Snow Lab, the Northern Hemisphere snow cover extent during February was 800,000 square miles below the 1981–2010 average. This was the third smallest February Northern Hemisphere snow cover extent in the 50-year period of record and smallest since 2002. The North American snow cover extent was the 13th smallest on record while the Eurasian snow cover extent was fourth smallest.
  

[AbruptSLR]

In the linked article Scribbler provides evidence for the position (that I support, see images) that the climate experience in February 2016 is: "…. a foretaste of what could very easily happen on a 5-15 year timescale in the annual measure if fossil fuel burning and related carbon emissions do not radically ramp downward."

http://robertscribbler.com/2016/03/16/one-month-above-1-5-c-nasa-data-shows-february-crossed-critical-threshold/

Extract: "… we’ve just experienced a month that was more than 1.5 C hotter than 1880s averages. It’s not a yearly average in this dangerous range — but likely the peak reading from a very intense El Nino combining with the growing base forcing of human climate change. That said, it’s a foretaste of what could very easily happen on a 5-15 year timescale in the annual measure if fossil fuel burning and related carbon emissions do not radically ramp downward."

[Theta]

In the linked article Scribbler provides evidence for the position (that I support, see images) that the climate experience in February 2016 is: "…. a foretaste of what could very easily happen on a 5-15 year timescale in the annual measure if fossil fuel burning and related carbon emissions do not radically ramp downward."

http://robertscribbler.com/2016/03/16/one-month-above-1-5-c-nasa-data-shows-february-crossed-critical-threshold/

Extract: "… we’ve just experienced a month that was more than 1.5 C hotter than 1880s averages. It’s not a yearly average in this dangerous range — but likely the peak reading from a very intense El Nino combining with the growing base forcing of human climate change. That said, it’s a foretaste of what could very easily happen on a 5-15 year timescale in the annual measure if fossil fuel burning and related carbon emissions do not radically ramp downward."

When we talk about ramping down Carbon Dioxide, would that include shutting down coal plants as well? Wouldn't the loss of global dimming, from discussions seen in the Aerosol thread, severely outweigh the benefits of stopping fossil fuel production? Or does the lack of fossil fuels emitted by humans outweigh the potential temperature rise (1 to 3C)

[Sigmetnow]

Includes a discussion of Svalbard warmth, and other impacts.

February Smashes Earth's All-Time Global Heat Record by a Jaw-Dropping Margin
By: Jeff Masters and Bob Henson, March 13, 2016

On Saturday, NASA dropped a bombshell of a climate report. February 2016 has soared past all rivals as the warmest seasonally adjusted month in more than a century of global recordkeeping. NASA’s analysis showed that February ran 1.35°C (2.43°F) above the 1951-1980 global average for the month, as can be seen in the list of monthly anomalies going back to 1880. The previous record was set just last month, as January 2016 came in 1.14°C above the 1951-1980 average for the month. In other words, February has dispensed with this one-month-old record by a full 0.21°C (0.38°F)--an extraordinary margin to beat a monthly world temperature record by. Perhaps even more remarkable is that February 2015 crushed the previous February record--set in 1998 during the peak atmospheric influence of the 1997-98 “super” El Niño that’s comparable in strength to the current one--by a massive 0.47°C (0.85°F).

http://www.wunderground.com/blog/JeffMasters/february-smashes-earths-alltime-global-heat-record-by-a-jawdropping

[Lord M Vader]

Dr. Jeff Masters is asking for anomalies higher than at Svalbard which averaged about 10^oC warmer for the period December to February.

My impression after looking at anomaly maps for those months is that both Franz Josef Land and Ostrov Vize at Vize Island both had an even bigger margin than Svalbard this winter.

Looking at Wundergrounds data and NOAAs values for the reference period 1961-1990 for November 2015 to February 2016, I get a rough estimated anomaly of a jaw-dropping

November: +15^oC

December: +8^oC

January: +17^oC

February: +11^oC

March: currently about +12^oC.

I suspect that the January value most likely is too high as a maximum value of +16C for January 12 is completely unrealistic and most likely a sign error. This means that the average of about -10  would have an anomaly of about 0,5-1 degree lower for January.

In any case, the anomaly for November 2015 to February 2016 is roughly an astonishing 12-13^oC higher than the average. If we suppose that March also will have an anomaly of 10-12^oC above normal, then a streak of FIVE MONTHS have had an anomaly of more than 10^oC(!!!)

Wundergrounds data (which are in whole degrees): http://www.wunderground.com/history/wmo/20069/2016/1/12/MonthlyHistory.html?&reqdb.zip=&reqdb.magic=&reqdb.wmo=

NOAAs data for statistical mean for Ostrov Vize:^{ftp://ftp.atdd.noaa.gov/pub/GCOS/WMO-Normals/TABLES/REG_II/RA/20069.TXT} 

Wikipedia have somewhat different averages for Vize Island but I don't put my belief into Wikipedia in this case. It mght have to do with a different base period for Wikipedias values which have been retrieved from Russia.

If anyone know what the station names at Franz Josef Land is it would be very interesting to see the anomalies from them as they also have been extremely high this winter.

Best, LMV

[AbruptSLR]

In the linked article Scribbler provides evidence for the position (that I support, see images) that the climate experience in February 2016 is: "…. a foretaste of what could very easily happen on a 5-15 year timescale in the annual measure if fossil fuel burning and related carbon emissions do not radically ramp downward."

http://robertscribbler.com/2016/03/16/one-month-above-1-5-c-nasa-data-shows-february-crossed-critical-threshold/

Extract: "… we’ve just experienced a month that was more than 1.5 C hotter than 1880s averages. It’s not a yearly average in this dangerous range — but likely the peak reading from a very intense El Nino combining with the growing base forcing of human climate change. That said, it’s a foretaste of what could very easily happen on a 5-15 year timescale in the annual measure if fossil fuel burning and related carbon emissions do not radically ramp downward."

When we talk about ramping down Carbon Dioxide, would that include shutting down coal plants as well? Wouldn't the loss of global dimming, from discussions seen in the Aerosol thread, severely outweigh the benefits of stopping fossil fuel production? Or does the lack of fossil fuels emitted by humans outweigh the potential temperature rise (1 to 3C)

Theta

First, you need to recognize that there is no world authority controlling mankind's response to the climate change hazard.  For one example, if China's air pollution is so bad that they cut aerosol emissions while only decreasing its carbon intensity rather than its total carbon emissions by 2030, then so that is going to be the way it is no matter what we say here.  For another example, if Obama can only limit carbon emissions by EPA restrictions on air pollution (rather than say by Congress approving a tax neutral carbon pricing plan) then that is also going to be the way that it is going to be and we all are going to have to live with the consequences, no matter how much happy talk that ESLD scientists provide in their public announcements.

Second, you need to realize that for a "wick problem" like climate change, the powers that be will not take effective action until necessity demands it (necessity is the mother of invention and natural selection).  The true of the matter is that we have been, and still are, generally following the 90 to 95% CL RCP 8.5 scenario, including its aerosol emissions pathway.  Also, due to the ECS, PDO, and nonlinear positive feedback risks, we may likely follow the RCP 8.5 temperature projection through 2050 even if we following the CoP21 pledges to the letter (which is unlikely), so your best plan of action is to develop a suitable adaptation plan for yourself, your family and those important to yourself.

Best regards,
ASLR

[jai mitchell]

When we talk about ramping down Carbon Dioxide, would that include shutting down coal plants as well? Wouldn't the loss of global dimming, from discussions seen in the Aerosol thread, severely outweigh the benefits of stopping fossil fuel production? Or does the lack of fossil fuels emitted by humans outweigh the potential temperature rise (1 to 3C)

to follow up with ASLRs comment, I do run across this from time to time.  It is a gut-check response.  In effect though the question you are asking is one of 3 things.

1.  Does this mean that we are screwed so badly that we might as well continue to pollute with coal keeping the near term rate of warming slower while we lock in even more warming in the future?

2.  Does this mean that we need to implement some kind of global dimming project that is not associated with GHG production (geoengineering)

3.  Does this mean that it doesn't really matter what we do (see 1 above).

The answers to this are

1>  What you don't realize is that the aerosols will go away sooner or later, either by our efforts or by massive climate induced destabilization and collapse.  The question is then: do you want to allow a slow death over the next 20 years and have a completely unlivable world (I am talking PETM warming here) in 50 years or do you want to have the warming experience now but reduce the future effects?  (I am for the latter)

2>probably

3>It may.  There is still massive uncertainty to the impacts of aerosols on the arctic, as well as a direct impact on the Lapse Rate feedback.  If some of this warming is indeed due to an economic cycle reduction in Chinese Aerosols (not just El Nino) then we are only now getting a taste of what is to come.  Some studies show that we are offsetting 50% of total radiative forcing from GHG with aerosols.  It is very possible that Michael Moore's 4.5ECS curve above is going to be the reality with a jump in temperatures to 3.5C by 2036.

[oren]

Yes we are screwed so badly is the short answer.
On the "positive" side, it is somewhat likely that collapse would include a war-induced nuclear winter, so it's a sort of natural negative feedback.

[AbruptSLR]

NOAA has issued their GMST report for February 2016 and it is much in line with NASA's report:

NOAA National Centers for Environmental Information, State of the Climate: Global Analysis for February 2016, published online March 2016, retrieved on March 18, 2016 from http://www.ncdc.noaa.gov/sotc/global/201602.

http://www.ncdc.noaa.gov/sotc/global/201602
&
http://www.ncdc.noaa.gov/sotc/summary-info/global/201602

Extract: "The February average temperature across global land and ocean surfaces was 2.18°F (1.21°C) above the 20th century average. This was not only the highest for February in the 1880–2016 record (surpassing the previous record set in 2015 by 0.59°F / 0.33°C), but it surpassed the all-time monthly record set just two months ago in December 2015 by 0.16°F (0.09°C). February 2016 also marks the 10th consecutive month a monthly global temperature record has been broken."


See also:
http://moyhu.blogspot.com/2016/03/noaa-global-feb-record-enso-comparison.html
Extract, with regards to the attached image: " As with GISS, I'll show the updated comparison with 1997/8. Again, it tracks closely, even with the dip in Jan and the peak in Feb. GISS was tracking in the range 0.4-0.5°C above 1997/8; NOAA is around 0.4. Both GISS and NOAA show a drop in March, back to about January levels. This seems less likely this time; with about half the month gone, the NCEP/NCAR index is still above Feb, although the early hot spell has subsided."

[AbruptSLR]

Yes we are screwed so badly is the short answer.
On the "positive" side, it is somewhat likely that collapse would include a war-induced nuclear winter, so it's a sort of natural negative feedback.

You might want to look at the two posts that I just put in the "Aerosol" thread in the "Science" folder that indicate that: (a) the Transient Climate Response, TCR, is significantly higher than AR5 projected due to the higher than expected negative forcing from aerosols; and (b) as China cleans-up its air pollution temperatures will definitely increase due to GHG that is already in the atmosphere; separately from the GMST increases due to new emissions.

[AbruptSLR]

I note that "Happy Talk" scientists like to compare the GMST impacts of our current Super El Nino to the 97-98 event, because it was followed by a La Nina event which makes the March GMST values less scary; however, our current Super El Nino has many more similarities to the 82-83 event (which was not followed by a La Nina); and the following table shows that in March 1983 the GISTemp was very close to the February GISTemp value (which was not the case in 1998).

NASA's GISTemp, base period: 1951-1980

Year   Jan  Feb  Mar     
1982    9   16   -2       
1983   52   40   42       
…
1997   32   36   50       
1998   60   88   61       
…
2015   81   87   90       
2016  114  135 ****   

[AbruptSLR]

The attached Karsten Haustein GFS 2m temp anom forecast issued March 18 2016, indicates that March 2016 could actually be slightly hotter than February 2016, if the current trend holds:

http://www.karstenhaustein.com/climate.php

[Lord M Vader]

ASLR, according to Tropical Tidbits, the SST anomalies have so far in March been higher than in February. The big question remains if we will seea rise in global anomalies for the last week of March. Personally I seriously doubt that March would get a bigger anomaly compared to February. Then I think it is more likely that it will be on 2nd or 3rd place.

[Sigmetnow]

I realize the U.S. is not "global," but:  NOAA's three-month outlook for June-July-August and September-October-November temperature probabilities are for warmer than normal -- most importantly in Alaska.

[Csnavywx]

Please note that the CFSv2 and CCSM4 both have serious initialization problems with their latest runs -- especially in the tropical Atlantic. These are incidentally also the only two models which do not completely decay the current Nino.

A Nina is strongly favored, but that doesn't necessarily mean a strong Nina is favored. However, the PDO is forecast almost universally by all of the remaining model suites to remain moderately to strongly positive.

[James Lovejoy]

My prediction for March, based on Nick Stokes data  through the 19th, and http://www.karstenhaustein.com/climate for the 20th through the 27th is that March GISS will almost certainly be the warmest March on the record, very likely (>95%)  have a smaller anomaly than February's, and very likely be a larger anomaly than any other previous month.  I'm guessing a central value of 1.25 +/- 0.10 (2sd).

Showing my work, Nick Stokes 1-19 avg 0.808 anomaly vs 1994-2013,
Karsten March 20-27 0.627 anomaly vs 1981-2010.  Average 0.754.  (Yes, not really valid to combine anomalies from two different eras, but results fall reasonably close to actuals, and as
the month goes on the errors become less and less important.)

[AbruptSLR]

My prediction for March, based on Nick Stokes data  through the 19th, and http://www.karstenhaustein.com/climate for the 20th through the 27th is that March GISS will almost certainly be the warmest March on the record, very likely (>95%)  have a smaller anomaly than February's, and very likely be a larger anomaly than any other previous month.  I'm guessing a central value of 1.25 +/- 0.10 (2sd).

Showing my work, Nick Stokes 1-19 avg 0.808 anomaly vs 1994-2013,
Karsten March 20-27 0.627 anomaly vs 1981-2010.  Average 0.754.  (Yes, not really valid to combine anomalies from two different eras, but results fall reasonably close to actuals, and as
the month goes on the errors become less and less important.)

Per the attached Karsten Haustein forecast through March 29 2016, your estimates for March may be erring slightly on the side of least drama due to the projected rapid increase in GMST towards the end of March.

[James Lovejoy]

AbruptSLR I believe my estimates are as accurate as possible with the information I have, and I try not to either understate or overstate where the data leads. 

BTW, the estimate through the 29th has dropped almost 0.01c to 0.746.  I'm still confident that the final value will end within the error bars.

[AbruptSLR]

AbruptSLR I believe my estimates are as accurate as possible with the information I have, and I try not to either understate or overstate where the data leads. 

BTW, the estimate through the 29th has dropped almost 0.01c to 0.746.  I'm still confident that the final value will end within the error bars.

James,

Thanks for the update, and I certainly was not intending to imply anything about the accuracy of your estimates; however, these numbers do seem to be subject to regular adjustment, and we will not know the official numbers until closer to mid-April.  Nevertheless, my point was that in the attached Karsten Haustein forecast through the end of March, the average temperature in March looks to be very close to the average temperature in February.

Best,
ASLR

[AbruptSLR]

This post could actually go into several different threads, but as the linked article is entitled: "February's Record Heat Astounds Scientists", I am placing it here.  That said, neither this National Geographic article, or any other article that I have seen, has pointed-out that the reason that the GMST effect of the current Super El Nino is atypically large (compared say to the 1997-98 Super El Nino), is because it came immediately after a near-El Nino event in 2014-15.  Further, I note that a fundamental projection of climate change models is that El Nino events become more frequent with increasing global warming; and that this increased frequency results in higher rates of increase for GMST (as occurred in 2015-16); and which is an indicator of a relatively high ECS value:

http://voices.nationalgeographic.com/2016/03/24/februarys-record-heat-astounds-scientists/

Extract: "The nearly six-tenths of a degree margin by which it beat the old February record, set last year, had federal scientists describing temperatures as “staggering.” That margin was confirmed by the National Aeronautical and Space Administration, which uses statistical techniques different than NOAA’s, as well as a University of Alabama Huntsville team and the private Remote Sensing System team, which relies on measurements from satellites.
“Yes, of course El Niño has a hand in the February and other monthly temperatures records we’ve been observing, but not the only hand, not even the winning hand,” Jessica Blunden of NOAA’s National Center for Environmental Information told Mashable. “During the last big El Niño event of 97/98, temperatures departures from average were much lower compared with what we’re seeing now with this comparable event, which shows us that general warming is occurring over time.”"

[Tor Bejnar]

From a response in Coverage bias and recent trends in global surface temperature, part 1 (emphasis added)

Deep Climate | January 21, 2016 at 10:45 am |
... it’s true that ONI was in El Nino territory (ONI >= 0.5) for the last couple of months of 2014. But it was in La Nina-ish (ONI <= -0.5) early on, and overall ONI was 0 for the year. Not only that, but global temperature usually lags ENSO by 3-4 months, and the last 3 months of 2013 saw a slightly negative ONI. So on balance I would say there was very little if any overall ENSO effect in 2014. 2015 definitely received a boost (like 1997), but the full effect should only be reached this year (as in 1998).

[AbruptSLR]

From a response in Coverage bias and recent trends in global surface temperature, part 1 (emphasis added)

Deep Climate | January 21, 2016 at 10:45 am |
... it’s true that ONI was in El Nino territory (ONI >= 0.5) for the last couple of months of 2014. But it was in La Nina-ish (ONI <= -0.5) early on, and overall ONI was 0 for the year. Not only that, but global temperature usually lags ENSO by 3-4 months, and the last 3 months of 2013 saw a slightly negative ONI. So on balance I would say there was very little if any overall ENSO effect in 2014. 2015 definitely received a boost (like 1997), but the full effect should only be reached this year (as in 1998).

Say what you want about the almost-El Nino of 2014, but at the attached NOAA PDF corrected Nino 3.4 forcast issued Nov 17 2014, the conditions set-up at the end of 2014 gave the 2015 Super El Nino a running start; and in ENSOs as in politics momentum is everything.

[AbruptSLR]

The following is a re-post from the "Modelling the Anthropocene" thread:

The linked (open access) reference takes into account the implications of the Paris Pact, and also uses ESLD assumptions about climate sensitivity; nevertheless, it projects radiative forcing scenarios that will likely result a commitment to eventually reach a 1.5C GMST rise by 2020 and a commitment to reach a 2C GMST rise by 2030:

Wagner L, Ross I, Foster J, Hankamer B (2016), "Trading Off Global Fuel Supply, CO2 Emissions and Sustainable Development", PLoS ONE 11(3): e0149406, doi:10.1371/journal.pone.0149406


http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149406

See also:
https://www.skepticalscience.com/dangerous-gw-sooner-than-thought.html

Extract: "University of Queensland and Griffith University researchers have developed a “global energy tracker” which predicts average world temperatures could climb 1.5C above pre-industrial levels by 2020."

[Buddy]

Another reflection of the warmth in the northern hemisphere through the first 85 days of the year.

http://climatechangegraphs.blogspot.com/2012/08/ratio-of-new-daily-record-high-temps-to_30.html

It's just not getting cold enough during the nighttime hours to get any record low temperatures.

And the "longer term view" (on a decade-by-decade basis) continues to worsen.  And in this view.....the "Arctic amplification" is evident at Canada and Russia warm more than the US.

This could likely set us up for yet another nasty fire season in the northern hemisphere this year.  Not good...    The feedback loops continue to kick in....

[Sigmetnow]

Jan-Feb-March-to-date average 2-meter temperature anomaly map.

@Weather_West:  "Check out those 10+ C (18+ F) anomalies in the Arctic. It's no wonder that #SeaIce reached record low this winter."

https://twitter.com/weather_west/status/714561450648477696

[AbruptSLR]

The attached Karsten Hautein GFS projection run on March 31 2016, makes it appear that the average GMST anom in March 2016 will be higher than that for February 2016.  If confirmed, this projection would indicate that we are in for yet another record, just one month after our last record breaking month.

[Lord M Vader]

ASLR, it's also interesting to see the forecasted decline in GSAT anomalies for the beginning of April. If it verifies, we can be virtually certain that the GSAT anomalies have peaked but will be followed by anomalously warm months ahead until July-August.

I doubt we'll see any daily anomalies from Nick Stokes higher than +0,90^oC for a good while. More likely that April-June will have anomalies in the range of 0,5-0,7^oC.

Best, LMV

[James Lovejoy]

The attached Karsten Hautein GFS projection run on March 31 2016, makes it appear that the average GMST anom in March 2016 will be higher than that for February 2016.  If confirmed, this projection would indicate that we are in for yet another record, just one month after our last record breaking month.

I'd give more weight to Nick Stokes's figures.  With 29 days of data in, he reports March's anomaly as almost a tenth degree less than February's.  Adjusting for his 94-13 base, and the fact that base has a few hundreds greater anomaly relative to GISS's 1951-1980 base for March relative to February, and my best estimate for GISS March is 1.29 +/- 0.10.  Likely cooler than February, extremely likely to be warmer than any other month in the record.

A more difficult question is 'what will the results be for the year'?

About six months ago I was of the opinion that 2016 would not be as much warmer than 2015 as 1998 was from 1997.  My logic was that the 2015 enso had gotten a running start from the near enso in 2014, and that some of the increase had already shown up in the 2015 record.

With the string of scorchers from October to March, I've modified this opinion.  As a first estimate, if the 2016 enso follows the 1998 decay pattern, then I'd guess the average anomaly for the year will be close to 1.00 (GISS), if it takes just a little longer to get to ENSO neutral range, it could be substantially warmer.  Only time will tell.

[Lord M Vader]

James, one thing that is interesting is that Tropical Tidbits shows a somewhat higher SST anomaly for March compared to February. http://www.tropicaltidbits.com/analysis/global.png

Given the land-ocean distribution, I think we will see a GISS March at 125+-0,10^oC.

The previous record warm March from 2010 will clearly be destroyed. Should be a decent possibility that both April and May will see new records.An eventual flip to La Niña will be crucial for the outcome of 2016 mean temperature anomaly.

Best, LMV

[Steven]

The attached Karsten Hautein GFS projection run on March 31 2016, makes it appear that the average GMST anom in March 2016 will be higher than that for February 2016.

The global mean temperature anomaly in Karsten Haustein's graph is about 0.82°C for February 2016 (monthly average), and 0.79°C for March 2016.  Both numbers are relative to baseline 1981-2010.  Those numbers are printed at the bottom left corner of the monthly mean maps on his website:

February 2016
March 2016

Also interesting is that the temperature anomalies in both the Arctic and the Antarctic were slightly lower in March 2016 than in February 2016.  So for those global temperature datasets that exclude the polar regions (e.g. JMA, NOAA and HadCrut4) the anomaly for March 2016 could possibly be slightly higher than for February 2016, but this is less likely for the datasets that include the polar regions (e.g. GISS).

For what it's worth, my naive guess for GISS for March 2016 is  1.26 +/- 0.07°C  (using linear regression on NCEP/NCAR data), which is very similar to Lord M Vader's and James Lovejoy's estimates.

[AbruptSLR]

For what it's worth, my naive guess for GISS for March 2016 is  1.26 +/- 0.07°C  (using linear regression on NCEP/NCAR data), which is very similar to Lord M Vader's and James Lovejoy's estimates.

Thank you.  It will be interesting to see the official numbers when they are released.

[BornFromTheVoid]

Roy Spencer reports a slight drop in global temps from last month, +0.83C to +0.73C, but still the warmest March on record.
http://www.drroyspencer.com/2016/04/uah-v6-global-temperature-update-for-march-2016-0-73-deg-c/

[Lord M Vader]

From Twitter, Ryan Maue reports that March was 0,07^oC lower than February. Anomaly was +0,63^oin March compared to +0,70^oC in February.

See https://twitter.com/RyanMaue/status/715949636914122754

Translated to GISS NASA we should end up somewhere between 1,2-1,3^oC above the 1951-1980 normal.

[AbruptSLR]

The linked (open access) commentary discusses the authors thinking about the "faux hiatus" (see attached image).  Evidently the commentary was written before the recent surge in GMST values:

http://web.science.unsw.edu.au/~matthew/nclimate2938.pdf

[James Lovejoy]

On Nick Stokes's blog, there's  a discussion of the March temperature.  From the discussion the anomaly varies from +.02 higher than Feb to -0.085 lower, with some of the discussion revolving around the reason for the discrepancy.  Link here http://moyhu.blogspot.com/2016/04/global-ncepncar-down-by-0085-still-hot.html

[James Lovejoy]

Another data point ESLR surface temperature time series shows 13.996 for March 2016, up 0.495 from March 2015.   This would make the March 2016 temperature anomaly the highest in the records.

No guarantee that this will be confirmed by the other temperature series, but alarming none-the-less.

[AbruptSLR]

The linked reference suggests  replacing linear regression with a new statistical approach for detecting climate change and provides an example applied to GMST data:

Aurélien Ribes, Francis W. Zwiers, Jean-Marc Azaïs & Philippe Naveau (06 April 2016), "A new statistical approach to climate change detection and attribution", Climate Dynamics, pp 1-20
 

http://link.springer.com/article/10.1007%2Fs00382-016-3079-6


Abstract: "We propose here a new statistical approach to climate change detection and attribution that is based on additive decomposition and simple hypothesis testing. Most current statistical methods for detection and attribution rely on linear regression models where the observations are regressed onto expected response patterns to different external forcings. These methods do not use physical information provided by climate models regarding the expected response magnitudes to constrain the estimated responses to the forcings. Climate modelling uncertainty is difficult to take into account with regression based methods and is almost never treated explicitly. As an alternative to this approach, our statistical model is only based on the additivity assumption; the proposed method does not regress observations onto expected response patterns. We introduce estimation and testing procedures based on likelihood maximization, and show that climate modelling uncertainty can easily be accounted for. Some discussion is provided on how to practically estimate the climate modelling uncertainty based on an ensemble of opportunity. Our approach is based on the “models are statistically indistinguishable from the truth” paradigm, where the difference between any given model and the truth has the same distribution as the difference between any pair of models, but other choices might also be considered. The properties of this approach are illustrated and discussed based on synthetic data. Lastly, the method is applied to the linear trend in global mean temperature over the period 1951–2010. Consistent with the last IPCC assessment report, we find that most of the observed warming over this period (+0.65 K) is attributable to anthropogenic forcings (+0.67 ± ± 0.12 K, 90 % confidence range), with a very limited contribution from natural forcings (−0.01±0.02 −0.01±0.02 K)."