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Sunday, June 23, 2013

Why is Global Warming Stagnating


SPIEGEL: Just since the turn of the millennium, humanity has emitted another 400 billion metric tons of CO2 into the atmosphere, yet temperatures haven't risen in nearly 15 years. What can explain this?
Storch: So far, no one has been able to provide a compelling answer to why climate change seems to be taking a break. We're facing a puzzle. Recent CO2 emissions have actually risen even more steeply than we feared. As a result, according to most climate models, we should have seen temperatures rise by around 0.25 degrees Celsius (0.45 degrees Fahrenheit) over the past 10 years. That hasn't happened. In fact, the increase over the last 15 years was just 0.06 degrees Celsius (0.11 degrees Fahrenheit) -- a value very close to zero. This is a serious scientific problem that the Intergovernmental Panel on Climate Change (IPCC) will have to confront when it presents its next Assessment Report late next year.


SPIEGEL: Do the computer models with which physicists simulate the future climate ever show the sort of long standstill in temperature change that we're observing right now?

Storch: Yes, but only extremely rarely. At my institute, we analyzed how often such a 15-year stagnation in global warming occurred in the simulations. The answer was: in under 2 percent of all the times we ran the simulation. In other words, over 98 percent of forecasts show CO2 emissions as high as we have had in recent years leading to more of a temperature increase.

SPIEGEL: How long will it still be possible to reconcile such a pause in global warming with established climate forecasts?

Storch: If things continue as they have been, in five years, at the latest, we will need to acknowledge that something is fundamentally wrong with our climate models. A 20-year pause in global warming does not occur in a single modeled scenario. But even today, we are finding it very difficult to reconcile actual temperature trends with our expectations.
Storch goes on to state two possibilities for incorrect climate models: (1) global warming gases (including CO2) have less of an impact than believed, or (2) climate scientists have underestimated the impact of natural causes of climate change. He also notes that too many climate researchers have approached the issue as "preachers," rather than scientists, and that the science is never settled. Read the whole thing.

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