Climate Sensitivity

Future Global Temperature Forecasts Trending Downward?


The Economist has published an intriguing table derived from a draft version of the Intergovernmental Panel on Climate Change's Working Group III that relates future projected global average tempertures to specific levels of carbon dioxide concentrations in the atmosphere. Here's the table:

Economist temperature data

For the record, current carbon dioxide atmospheric concentrations are just shy of 400 parts per million. This table is related to the important issue of climate sensitivity which is generally defined as how much warming would eventually occur as a result of doubling carbon dioxide concentrations in the atmosphere. With regard to the data in this table, the Economist notes:

According to one table from the unpublished report, which was seen by The Economist (above), at CO2 concentrations of between 425 parts per million and 485 ppm, temperatures in 2100 would be 1.3-1.7°C above their pre-industrial levels. That seems lower than the IPCC's previous assessment, made in 2007. Then, it thought concentrations of 445-490 ppm were likely to result in a rise in temperature of 2.0-2.4°C.

The two findings are not strictly comparable. The 2007 report talks about equilibrium temperatures in the very long term (over centuries); the forthcoming one talks about them in 2100. But the practical distinction would not be great so long as concentrations of CO2 and other greenhouse-gas emissions were stable or falling by 2100. It is clear that some IPCC scientists think the projected rise in CO2 levels might not have such a big warming effect as was once thought.

Still, over the past year, several other papers have suggested that views on climate sensitivity are changing. Both the 2007 IPCC report and a previous draft of the new assessment reflected earlier views on the matter by saying that the standard measure of climate sensitivity (the likely rise in equilibrium temperature in response to a doubling of CO2 concentration) was between 2°C and 4.5°C, with 3°C the most probable figure. In the new draft, the lower end of the range has been reduced to 1.5°C and the "most likely" figure has been scrapped. That seems to reflect a growing sense that climate sensitivity may have been overestimated in the past and that the science is too uncertain to justify a single estimate of future rises.

One implication of these data is that humanity may have more time in which to prepare for whatever global warming may occur. A caveat: The data is still from a draft report and can change.

I have been reporting on the research trend toward lower climate sensitivity estimates for some time. To catch up go to Reason's climate sensitivity tag for more background.

NEXT: Judge Halts Detroit Bankruptcy Proceedings

Editor's Note: We invite comments and request that they be civil and on-topic. We do not moderate or assume any responsibility for comments, which are owned by the readers who post them. Comments do not represent the views of or Reason Foundation. We reserve the right to delete any comment for any reason at any time. Report abuses.

  1. Fucking ice age. I knew it. I hate blubber.

    1. OK, PL, YOU get to shovel the sidewalk.

      1. And goddamned fur. It smells.

        Tampa is, at least, south of the glacial regions.

      2. Dammed Deniers. Don’t they know that the Science is settled?

    2. As long as it’s proportional and accentuates the natural curves, a little extra weight isn’t a datebreaker.

  2. Future Global Temperature Forecasts Trending Downward?

    Does anyone other than climate hustlers care?

    1. Anyone with significant energy expenditures would care, I imagine.

  3. Climate Forecast Change must be stopped. Think of the severe impact it will have on poor scientists trying to get NSF grants.

  4. What difference, at this point, does it make? Climate change is a political entity divorced from its scientific roots; even if the research turns over and its former backers back off, it will continue as a policy recommendation for the rest of this decade and likely continue to be a manipulable factor in the voting habits of a generation of leftists. No mere revision of the data, not even by its foundational body, will derail the thing.

    1. Wasn’t that the point? I mean, why else go full court press on the political propaganda machine about “global warming” or “climate change” if not to do this?

      1. You have to wonder how long temperatures will have to be stable or fall before the Climate Krampuses go “Ohhhhhhh, that’s right, this is good news.”

        I predict that it will be 10 minutes before the glaciers devour their homes.

        1. I predict that it will be 10 minutes before the glaciers devour their homes

          Ha ha, I wouldn’t doubt it.

      2. Summer is the right time to demagogue AGW. At least they got the timing right, unlike Gore’s Copenhagen fiasco.

  5. Multi-decadal variation of the East Greenland Sea-Ice Extent: AD 1500-2000

    Knud Lassen and Peter Thejll

    Abstract: The extent of ice in the North Atlantic varies in time with time scales stretching to centennial, and the cause of these variations is discussed. We consider the Koch ice index which describes the amount of ice sighted from Iceland, in the period 1150 to 1983 AD. This measure of ice extent is a non-linear and curtailed measure of the amount of ice in the Greenland Sea, but gives an overall view of the amounts of ice there through more than 800 years. The length of the series allows insight into the natural variability of ice extent and this understanding can be used to evaluate modern-day variations. Thus we find that the recently reported retreat of the ice in the Greenland Sea may be related to the termination of the so-called Little Ice Age in the early twentieth century. We also look at the approximately 80 year variability of the Koch [sea ice] index and compare it to the similar periodicity found in the solar cycle length, which is a measure of solar activity. A close correlation (R=0.67) of high significance (0.5 % probability of a chance occurrence) is found between the two patterns, suggesting a link from solar activity to the Arctic Ocean climate.

    1. We consider the Koch ice index

      I KNEW it!

  6. I told you guys you’re going to regret call for a border fence with Mexico. They ARE going to use it to keep us in when the glaciers start heading south again.

    1. Hey, you want the nuclear option? We can fix ya right up!

  7. Its the charge on the electron all over again.

Please to post comments

Comments are closed.