extended the y scale a bit s. widening the x-axis. It could be confusing.
A couple of thoughts on the product distribution chain, the reachable target audience and effective communication.
-- If just forum readers, then there are few constraints on size. The graph is inherently too complex to fit the 700 pixel dimensional constraint, ditto for the extended width with scroll bar. However it is not an animation so file size will be small even if it is 1500 pixels wide png or jpg. In that case, the forum will resize it by unknown means* to 700 pixels width and that must be intriguing enough that viewers will click on to the full size.
-- If post-forum to say Twitter, posters like Zack are able to distribute up to 1800x1200 images via that medium. The normal Twitter image on my monitor is 503x336. The larger format allowed would insure that your graphic could be distributed intact.
Note poor programming at Twitter HQ has lead to jpg:large in url terminations which browsers are processing to jpg-large which is an invalid file format not recognized by other software (until the -large is removed). This is likely related to bad programming at Twitter that is causing failure of contextual mouse menus, ie copy/paste, in their re-bundling of .mov to html5 'GIF'. It may however be intentional, to wall off Twitter from the rest of the internet, forcing people into its 'ecosystem'.
-- The WaPo is the last remaining English-language newspaper in the US covering climate change and weather at any depth and likeliest to cover significant developments. The graphic would not work at all in the WaPo print edition. Most people however would see it online, probably on an iPhone or similar with 'retinal' resolution but nonetheless tiny image (very little physical screen width).
The WaPo would reproduce the image accurately and link in to the forum original. For that reason, careful explanatory text -- even of the obvious -- is important. Also explanation of potential confusing aspects. Most other online sources like buzzfeed would simply copy the WaPo article but there's no assurance or control over image size retention or links to original context.
*Below is one of Zack's high quality Twitter images. I'm just checking here to see how the forum thumbnails large images down. That can be done by subtracting the thumbnail from the four common reductions schemes (bicubic, sinc, bilinear, none) to see if it is any of those. It might instead be lossy jpg compression in which case it won't rescale back to the original size.
So far it's emerged that the forum allows an additional 74 pixels (to 774 width) in its scroll bar configuration (which may be related to mac vs dos dpi differences of 72 vs 78). Twitter, on an iMac at 'actual size' in Opera browser, shows the thumbnail as 505x338 which includes a 1 pixel boundary of 230 gray and slightly rounded corners that chop off any information that was there in the original. Zack's 1800x1200 reduces correctly in gimp to 700 x 467 (ie 466.66667) whereas the forum reduces it to 700x467. The forum has oddly offset the title line by 11 pixels vertically and has utilized lossy compression.
In summary, it's difficult to predict what viewers see because of device variations and different choices made at Twitter, Simple Machines, browser designers and device hardware. However as long as viewers are willing to download an intact original, the potential is there to preserve scientific accuracy in the chain of transmission.