Media Warming Confusion

You may already have seen some of these misleading headlines:

The UK Telegraph says, “Global warming may 'stop', scientists predict” — “… Researchers studying long-term changes in sea temperatures said they now expect a ‘lull’ for up to a decade.”

National Geographic News blares, “Cooler Climate May Hit N. America, Europe Next Decade.”

The New York Times wonders, “Can Climate Campaigns Withstand a Cooling Test?” and says that the Nature study forecast “some Northern Hemisphere cooling in the coming decade.”

Unfortunately, that's not the real story. Those headlines misreport what the cited studies -- and the scientists who performed them -- actually said.

For an explanation, we'll turn to environmental scientist Joseph Romm, author of the Climate Progress blog:

None of these headlines accurately portray what the data presented actually says. Let’s look at the paper’s key figure, the one that looks at past and (forecast) future global temperatures:

[click image to enlarge]

Let me try to explain this complicated figure.

The first thing to know — indeed, one major source of confusion — is that “each point represents a ten-year centred mean.” That is, each point represents the average temperature of the decade starting 5 years before that point and ending 5 years after that point.

Second, the red line is the actual global temperature data from the UK’s Hadley Center for Climate Prediction and Research. Why does the red line stop in 1998 and not 2007? Again, it is a running 10-year mean, and the authors use data from a Hadley paper that ends around 2003 (I believe), so they can’t do a ten-year centered mean after 1998.

Third, the black line is one of the IPCC scenarios, A1B. It is a relatively high-CO2-growth model — but actual carbon emissions since 2000 have wildly outpaced it (see here).

Fourth, the solid green line is the “hindcast” of the authors — how well their model compares to actual data (and the A1B scenario). It is then extended (in dashes) through 2010 and finally to 2025, where it meets up with A1B, since their model only imposes decadal variability on the inexorable climb of human-caused global warming.

Fifth, the short purple line is with radiative forcing (i.e greenhouse gas concentrations) frozen at 2000 levels, which, of course, didn’t happen.

So you can clearly see that the green line rises and then plateaus, repeatedly, until it really starts to take off in the decade of the 2010s. Perhaps the source of much of the media’s confusion is that the authors describe their results in the final line of the abstract this way:

Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.

But what they mean by that statement is not what a simple reading of that sentence would suggest:  They do not mean that “the global surface temperature may not increase over the next ten years starting now.” What they mean is what the lead author, Dr. Noel Keenlyside, wrote me last night when I asked for a clarification:

Thus, based on our results we don’t expect an increase in the mean temperature of the next decade (2005-2015).

They are predicting no increase in average temperature of the “next decade” (2005 to 2015) over the previous decade, which, for them, is 2000 to 2010! And that’s in fact precisely what the figure shows — that the 10-year mean global temperature centered around 2010 is the roughly the same as the mean global temperature centered around 2005.

The authors have not predicted the next 10 years won’t see any warming...

I recommend you read Romm's whole article if you want to really understand what the data means.

Mike Treder

Comments

[Mick]

http://www.spaceweather.com/

The sun god would like a word in on this too.

[Tom Craver]

The green mean point for 2000 - based on modeling with real "hindsight data" in 2005, if I understand it correctly - is substantially below the actual temperature in 1998.

Doesn't that mean that temps after 1998 must be substantially lower, in order for that green "mean" point to be so low? Even their projected green point is lower.

And why did they plot a 10 year mean only every 10 years, rather than doing a running 10 year mean? That would have let them plot real data past 1998, giving a more accurate picture of what is happening,