long term climate feedback loop
August 6, 2013

Climate Scientist Warns Of Long-Term Climate Feedback Loop

Brett Smith for redOrbit.com - Your Universe Online

According to University of Hawaii at Manoa oceanographer Richard Zeebe, future warming due to the current burning of fossil fuels will cause the Earth's global temperatures to rise longer than expected.

In his report, which was published in Proceedings of the National Academy of Sciences, Zeebe looked at the long-term climate effects of today's human activity thousands of years into the Earth's future.

"When we talk about climate sensitivity, we're referring to how much the planet's global surface temperature rises for a given amount of CO2 in the atmosphere," he said.

Modern-day climate sensitivity is typically pegged at approximately a 3-degree Fahrenheit rise in temperature per doubling of atmospheric carbon dioxide. However, this ratio could change over the millennia with disastrous results, Zeebe said.

Using information on past climate conditions, Zeebe determined slow climate feedbacks could boost climate sensitivity and magnify warming. Climate feedback, like audio feedback sometimes heard on a public address system, is when a system recursively acts on itself, amplifying an audio signal into a loud, piercing tone in the case of a PA system.

With respect to climate, feedback can occur via fluctuations in temperature, snow cover and sunlight. When rising temperatures melt snow, it typically exposes a darker surface that reflects less and absorbs more sunlight. The greater absorption of sunlight leads to additional warming and so on, creating a feedback loop.

Zeebe noted previous studies have tended to focus on short-term feedbacks that involve factors like snow cover or clouds. Instead, the Hawaii-based scientist looked at long-term feedback, as determined by land ice or vegetation, and potential changes to climate sensitivity over time.

"The calculations showed that man-made climate change could be more severe and take even longer than we thought before," Zeebe said. He noted while some of these processes take place over centuries or millennia, this only means the consequences could be considerably difficult to reverse in the short term.

"Politicians may think in four-year terms but we as scientists can and should think in much longer terms," Zeebe said. "We need to put the impact that humans have on this planet into a historic and geologic context.

"By continuing to put these huge amounts of carbon dioxide in the atmosphere, we're gambling with climate and the outcome is still uncertain," he added. "The legacy of our fossil fuel burning today is a hangover that could last for tens of thousands of years, if not hundreds of thousands of years to come."

Since the industrial revolution of the 19th century, the burning of fossil fuels has increased the amount of atmospheric carbon dioxide by more than 40 percent over its pre-industrial concentration of 280 parts per million.

In May, climatologists marked a dubious milestone - the atmospheric carbon dioxide concentration passed 400 ppm for the first time since man's emergence on the planet. Many scientists predict the current concentration of carbon dioxide will have a significant and lasting impact on Earth's climate, including considerable sea level rise due to the melting of the Greenland ice sheet.