Scientists spar over cause of warming, agree on its occurrence
“In my mind, humans have contributed to climate change,” Muller continued. “The real issue is how much.”
Most climate scientists say that human activities are a major — if not the major — factor driving changes to temperature and weather patterns, but Muller told Markey and Waxman he was not convinced of that yet. There are still unanswered questions about the role the sun and ocean currents may play in causing those patterns, he said.
In fact, only half of the warming observed in the past 50 years may be linked to human emissions from the use of fossil fuels and other activities, he said. “Then we have much more time to prepare and adapt than we do if it’s 100 percent” he added.
Muller said that a mode of variability occurring in the North Atlantic Ocean called the Atlantic multidecadal oscillation (AMO) may be playing a larger role then most climate scientists realize. The sun was also a problem, he said, noting that scientists assume that solar activity drove early 19th century warming before industrial emissions were a leading factor.
“I believe we do not understand why the variation in sunspots affects the climate as much as it does,” he said. “I think that we have to look at the AMO again and reconsider whether it could be having an effect just as the sun has an effect without us understanding how,” he added.
But two other scientists who had been asked to address the panel — William Chameides, vice chairman of a study authorized in the last Congress called America’s Climate Choices, and Ben Santer, a research scientist at the Lawrence Livermore National Laboratory — said that those hypotheses had already been tested.
“It’s really not rocket science,” said Chameides. “It’s looking at the possible explanations and looking at actual observations to eliminate them.”
Oceans around the world have warmed in the past decades, Chameides noted. If they were contributing energy to the atmosphere and not absorbing any new energy to replace it, one would not expect to see oceanic temperatures rise.
Santer said the observed pattern of warming in the first atmospheric layer — or troposphere — and cooling in the layer above that — known as the stratosphere — is difficult to reconcile with a theory of natural causation.
“We know of no mode of natural climate or natural climate variability that could generate that kind of pattern,” he said, adding that it is exactly what would be expected in response to human-caused changes to atmospheric composition.
‘Not an excuse for inaction’
Chameides said that continued uncertainty about certain details of climate science should not dampen interest in carbon mitigation.
“The fact that we cannot predict the future with perfect accuracy is not an excuse for inaction,” he said. “It rarely is in other arenas.”
Just as a car owner might feel reassured that his vehicle has airbags — even though he may never need them — so should policymakers take actions now to reduce greenhouse gas emissions, he said. He noted that policies that are later found to be unnecessary or ineffective can change, but it might be more difficult to reverse severe climate change once it has been set in motion.
This back and forth was witnessed only by Waxman and Markey — the ranking members of the Energy and Commerce and Natural Resources committees respectively.
The two men shepherded a bill through the House two years ago that would have capped industrial greenhouse gas emissions, but it stalled in the Senate.
Since then, Waxman said, “the House has voted 21 times to block actions to address climate change.”
Waxman requested a hearing last week in his own committee, but he said panel Chairman Fred Upton of Michigan and other senior Republicans had not responded to that request.
“A common refrain I hear on the Energy and Commerce Committee is that the science is ‘not settled,'” Waxman said. “But at the same time that committee Republicans argue that the science is unresolved, they have rejected multiple requests to bring scientists before the committee to educate members.”
He noted that Republicans had also passed several amendments to strip funding for climate science initiatives within the federal government, including at NASA.