Climate sensitivity means we’re in bigger trouble than we thought

The news on the climate sensitivity has gotten a little worse, as researchers have just concluded that while the Earth continues to warm up, it actually becomes more sensitive to rising carbon dioxide levels in the atmosphere, effectively speeding up global warming. The result is a planet that by the year 2100 will be 5.9 degrees Celsius hotter than pre-industrial levels, a mark that hasn’t been reached on Earth in three-quarters of a million years.

The term is climate sensitivity and it’s used to describe the way that the Earth responds to a given change or impact, such as an increase in carbon dioxide levels, that affects average temperatures. The idea is that any rise or fall in global temperatures will entail a set of feedbacks that will amplify the effects of said rise or fall. That amplified change is thus a measure of the planet’s climate sensitivity.

Needless to say, projections of how sensitive the Earth will be over the upcoming years to the continuing, human-caused increases in atmospheric C02 levels are of vital interest and concern. If we double the amount of carbon dioxide in the atmosphere – an ignoble feat we’re about halfway through accomplishing – evidence shows that the average surface temperature on Earth will rise 1.2 degrees based on that extra C02 alone. But factor in feedback mechanisms (extra water vapour in the atmosphere, ice melting at the poles, for example) and the climate-sensitive increase is more likely to be around three degrees. Or so we thought.

A new study led by Tobias Friedrich from the University of Hawaii’s International Pacific Research Center concludes that those estimates are unrealistic and that a 5.9 degree increase by the end of the century is the more likely scenario, based on current production levels of C02. Researchers looked at ice cores and ocean sediment samples to map Earth’s previous record for climate sensitivity over the past eight glacial periods, going back 784,000 years. What they found was that as the Earth gets warmer, it becomes more sensitive to increases in atmospheric C02.
“Our results imply that the Earth’s sensitivity to variations in atmospheric CO2 increases as the climate warms,” says Friedrich. “Currently, our planet is in a warm phase—an interglacial period—and the associated increased climate sensitivity needs to be taken into account for future projections of warming induced by human activities.”

The result would be catastrophic for life on Earth. “The projected effects of greenhouse gas emissions such as sea-level rise, ice melt, coral bleaching, ocean acidification etc. could be devastating not only for our environment but also for our food supply, our economy, and the livelihood of our planet in general,” says Friedrich, who adds that “the only way out is to reduce greenhouse gas emissions as soon as possible.”

One of the most well-known feedback mechanisms is water vapour, which is said to build up in higher and higher concentrations in the atmosphere as the planet heats up, contributing in its own right to the global warming process. Another is the melting of ice and permafrost at the poles, which will release further stores of carbon and methane into the atmosphere. Indeed, the sea ice in Canada’s Arctic has been hit extremely hard, with this year’s readings showing the lowest winter maximum ice on record and the second lowest summer minimum on record.

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