‘Effect CO2 op opwarming is erger dan we dachten’

1 jun i 2016 – De New Scientist wilde weten wat de laatste temperatuurgegevens betekenen in de klimaatmodellen. ‘Do the results still stand given the record warming in 2014, 2015 and 2016?’ Het antwoord is ‘neen’, het is erger dan we al dachten.

Uit het bericht van de News Scientist
‘(…) New Scientist asked those behind the studies what would happen if the latest global temperature data was plugged into their models.
One headline-making 2013 study had concluded that the immediate warming that would result from a doubling of CO2 in the atmosphere would be around 1.3 °C – significantly less than most previous estimates. If correct, this would mean we still have a chance of limiting warming to below the “dangerous” point of 2 °C despite soaring CO2 levels.
But this was before global temperatures shot past 1 °C above pre-industrial levels last year, as predicted by New Scientist in July 2015. If the 2013 study was repeated using that value, it would give an estimate for the immediate warming of 1.6 °C, says Piers Forster, one of the study’s authors based at the University of Leeds, UK.

Record-breaking tempertures
If we assume that the average global surface temperature in 2016 will be a record-breaking 1.3 °C above the pre-industrial level, as expected, the estimate would be closer to 2.1 °C, Forster says. But that may be an overestimate due to the current spike in warming caused by a now-fading El NiÑo. “Maybe 1.6 °C is closer to the ‘truth’,” he says. Indeed, he points out that 1.6 °C is well within the uncertainty bounds of his 2013 study.

Even before the recent warming, several other studies had already concluded that the 2013 estimate of the immediate warming effect was too low. These suggested that Forster’s team underestimated how much warming has been masked by the cooling effect of other pollutants, such as sulphur aerosols, that we pump out alongside CO2.

In 2014, Drew Shindell of Duke University concluded that the immediate warming in response to a doubling of CO2 would be around 1.7 °C. A 2015 study by a team including Gavin Schmidt of the NASA Goddard Institute for Space Studies in New York got the same result. And this year, Trude Storelvmo of Yale University put it at an alarming 2 °C.

Worse still, none of these later studies used any temperature data from after 2010. If they were repeated with the latest data, Shindell, Schmidt and Storelvmo all say the estimated value would be a little higher. “The estimate would probably be slightly higher if we had included data up to the present,” Storelvmo says. “We are in the process of doing that.” Only Shindell put a number on how much higher, guestimating that his approach would produce a value of 1.8 rather than 1.7 °C.

The reason these estimates are only slightly higher despite the record warming we have seen over the past couple of years is because the study methods were designed to minimise the effect of short-term temperature variations.

“Another few years of similar values will be another story,” Schmidt says. In other words, if rapid warming continues in the longer term – perhaps after a slight fall in 2017 due to the effects of La NiÑa – all estimates of climate sensitivity based on the warming over the past century would increase considerably. (…)’

New Scientist, 25 mei 2016: Effect of CO2 on warming is worse than we thought

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