Monday, May 28, 2012

11 F Warming by 2050?? No way.

Note added 5/31/12: Reuters has issued a correction to the article this post was based on. Click here for details.
The new Romm Record of 11°F apparently comes from a Reuters article where Faith Fatih Birol, the chief economist of the IEA, says we are on track for that amount of warming by 2050:
"When I look at this data, the trend is perfectly in line with a temperature increase of 6 degrees Celsius (by 2050), which would have devastating consequences for the planet," Fatih Birol, IEA's chief economist told Reuters.
That seems preposterous to me, on its face and on further analysis, which seems to me implies an additional warming (from now) of about 1.5 to 2°F by 2050. Here's why.

The carbon-climate response (CCR) is about 1.5°C per trillion metric tons of carbon emitted. That's the number given in the recent Swart and Weaver Nature Climate Change paper analyzing expected from the Alberta tar sands, with a range of 1.0–2.1 °C per Tt C (5th–95th percentile). That result comes from a 2009 Nature paper by Matthews et al., and this function includes feedbacks.

So let's add up the emissions.

Fossil fuels and cement production: 
Here is historical carbon emissions data from CDIAC; it includes fossil fuel combustion and cement production, and comes to 347 GtC as of 2008. Add in the recent IEA figures -- which are for fossil fuel consumption only -- and using the CDIAC data to estimate cement-carbon for the last few years, and the total emissions in that sector are about 375 GtC.

Land use changes:
Here is CDIAC's estimates of carbon emissions from land use changes. It the 1800s it was several times combustion emissions, but since 1933 it has been less and is now about 16% of combustion emissions. Add these up and this sector's total emissions (since 1850) are about 165 GtC.

Total Emissions:
So total emissions since 1850 are about 540 GtC, for which the CCR gives an expected warming of 0.81°C , which is what's been observed. Here's the plot:

So cumulative emissions by 2050 look to be around 2000 GtC, give or take. [That's the upper limit of applicability of this CCR.] That gives an expected [total] warming of about about 3°C (2.2°C more than today), or a total of 5.4°F, half of Birol's number.

Even that seems large. It means the next 38 years will see an average temperature increase of 0.58°C/decade, which is three and a half times the GISS warming rate of the last 30 years. Be honest: does that seem likely to you?

Even taking the upper bound of the CCR range, 2.1°C (which, let's note, overestimates the warming that's taken place so far by over 30%), gives a total warming of 7.6°F -- an additional warming of 0.9°C/decade from now until 2050.

I just don't see how anyone can get 11°F out of these numbers. 2050 cumulative emissions would need to be about 3,500 GtC for that to happen, which seems very unlikely. (At the CCR's upper bound it would be 2,500 GtC, which seems unlikely, though perhaps not "very" unlikely.)

Conclusion: Romm is rong -- in this case, the "alarmist" label definitely applies.

Note added: On second thought, 2050 cumulative emissions could be much less than I assumed -- projecting the line in the plot above, starting at 1950, gives cumulative emissions of 1300 GtC in 2050, not 2000 as I guessed. That gives a total warming of only 3.5°F (2.0°C) by 2050.


Anonymous said...

Perhaps this is what he has in mind

From abstract:

The Massachusetts Institute of Technology (MIT) Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model’s first projections were published in 2003, substantial improvements have been made to the model, and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections; for example, the median surface warming in 2091–2100 is 5.1°C compared to 2.4°C in the earlier study. Many changes contribute to the stronger warming; among the more important ones are taking into account the cooling in the second half of the twentieth century due to volcanic eruptions for input parameter estimation and a more sophisticated method for projecting gross domestic product (GDP) growth, which eliminated many low-emission scenarios.

David Appell said...

That study gives warming of 9 F by 2190, not 11 F by 2050. Huge difference.

And why focus on just one model, instead (as do Matthews et al) an ensemble of them? Many other models give far lower results.

climatehawk1 said...

And again, Romm did not say 2050, as I noted in my comment on your previous post on this.

Anonymous said...

You mean 9F (5C) by 2100? That's the median answer, as highlighted. Under BAU they see to call for about 40% shot at 6C (11F) or higher. And, as Eli pointed out, Romm makes no mention of 2050.

The MIT paper isn't the last word, but Romm hardly pulled the number out of the air.

n2 said...

The Reuters article has 2050 in brackets implying that the journalist added that for clarification but perhaps the person being quoted did not say it?

2050 could just be the wrong date.

tonylearns said...

Romm's article doesn't give any time limit, so it could even be for after 2100. The exact quote from Birol is "“the trend is perfectly in line with a temperature increase of 6 degrees Celsius [11°F], which would have devastating consequences for the planet.” To me that implies an ultimate warming of 6°C.
Why on earth would you attribute something to someone based on something a reporter from Reuters posted without checking?
frankly I consider 6°C unlikely in any scenario, but it is not out of the realm of reasonable possibility.

Frontiers of Faith and Science said...

POinting examples of Romm using inflammatory hype to make his points is an endless job.

David Appell said...

Tony: Check the Reuters article again -- the quote by Birol includes "by 2050" in parentheses, indicating it was the context of his discussion with the journalist.

David Appell said...

Tony: Reuters is a very reputable news agency.

Second, I have written to Faith Birol, asking for his carbon-climate response function, but haven't (yet) received a reply.

climatehawk1 said...

The fact that Reuters is a reputable news agency does not mean they don't get things wrong. In this case, it seems pretty clear to me that they did.

Anonymous said...

Anonymous said...

Why no second "update" to this post, with your acknowledgement that Reuters made a mistake in that its reporter erroneously inserted the "(by 2050")" date, when Birol meant "by near the end of the century", as you've acknowledged in a separate(non-linked)post??

David Appell said...

Anon 9:22 -- good idea, thanks. I'll add one.