Given that, no one is going to like new University of Washington claims that it's already too late. People who want curbs on emissions won't like news that it won't help and people who don't think emissions are the biggest problem in a worldwide recession won't bother to listen if it doesn't matter.
But there is at least a glimmer of hope. While there would continue to be warming even if the most stringent policy proposals were adopted, because there still would be some emission of heat-trapping greenhouse gases such as carbon dioxide and methane, the claim that even if all emissions were stopped now, temperatures would remain higher than pre-Industrial Revolution levels because the greenhouse gases already emitted are likely to persist in the atmosphere for thousands of years has some room for interpretation - because accurate temperature records don't even go back 40 years much less 140 years.
But first, the bad news; Kyle Armour, a UW doctoral student in physics, says it is possible temperatures would continue to escalate even if all cars, heating and cooling systems and other sources of greenhouse gases were suddenly eliminated, because 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 said. Armour is the lead author of a paper documenting the research, published recently in Geophysical Research Letters.
If global warming skeptics stated the global temperature, whatever that means, was 1.5 degrees Fahrenheit lower than it was before the Industrial Revolution, climate scientists would have a field day with the inaccuracy of measurement techniques available before the recent past. So stating that 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, has to be treated with some skepticism. Their calculations took into account the perceived 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 their best-case simulation, the global temperature would actually decline, but it would remain about a half-degree higher than pre-Industrial Revolution levels and probably would not drop to those levels again, Armour said. 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. Far beyond what IPCC models have projected.
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 said.
But uncertainties do not lessen the importance of the findings, he said. They remain 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.
Of course it is not realistic to expect all emissions to cease suddenly, and Armour notes that the overall effect of aerosols – particles of sea salt or soot from burning fossil fuels, for example – is perhaps the largest uncertainty in climate research. So any simulation will have room for interpretation.
As emissions of greenhouse gases continue, the "climate commitment" to a warmer planet only goes up, Armour said. 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 said. "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."