climate change

Committed to a hotter climate

U. WASHINGTON-SEATTLE (US) — If all greenhouse gas emissions stopped today, it’s possible temperatures on Earth would continue to climb.

New work by researchers at the University of Washington—reported in the journal Geophysical Research Letters—suggests that the world is committed to a warmer climate because greenhouse gases already emitted are likely to persist in the atmosphere for thousands of years.

Kyle Armour, a doctoral student in physics, says even if all cars, heating and cooling systems, and other sources of greenhouse gases were suddenly eliminated temperatures might continue to escalate. The reason: Tiny atmospheric particles called aerosols, which tend to counteract the effect of greenhouse warming by reflecting sunlight back into space, would last only a matter of weeks once emissions stopped, while the greenhouse gases would continue on.

“The aerosols would wash out quickly and then we would see an abrupt rise in temperatures over several decades,” he says.

The global temperature is already about 1.5 degrees Fahrenheit higher than it was before the Industrial Revolution, which began around the start of the 19th century. The scientists’ calculations took into account the observed warming, as well as the known levels of greenhouse gases and aerosols already emitted to see what might happen if all emissions associated with industrialization suddenly stopped.

In the best-case scenario, the global temperature would actually decline, but it would remain about a half-degree F higher than pre-Industrial Revolution levels and probably would not drop to those levels again, Armour says.

There also is a possibility temperatures would rise to 3.5 degrees F higher than before the Industrial Revolution, a threshold at which climate scientists say significant climate-related damage begins to occur.

The scientists are confident, from the results of equations they used, that some warming would have to occur even if all emissions stopped now. But there are more uncertainties, and thus a lower confidence level, associated with larger temperature increases.

Climate models used in Intergovernmental Panel on Climate Change assessments take into consideration a much narrower range of the possible aerosol effects, or “forcings,” than are supported by actual climate observations, Armour says. The Nobel Peace Prize-winning panel, sponsored by the United Nations, makes periodic assessments of climate change and is in the process of compiling its next report.

As emissions of greenhouse gases continue, the “climate commitment” to a warmer planet only goes up, Armour adds.

He believes it is helpful for policy makers to understand that level of commitment. It also will be helpful for them to understand that, while some warming is assured, uncertainties in current climate observations—such as the full effect of aerosols—mean the warming could be greater than models suggest.

“This is not an argument to say we should keep emitting aerosols,” he says. “It is an argument that we should be smart in how we stop emitting. And it’s a call to action because we know the warming we are committed to from what we have emitted already and the longer we keep emitting the worse it gets.”

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