“Scientists have been hammering governments with the evidence for several decades, and it’s incontrovertible,” Princeton University climate scientist Michael Oppenheimer said. “Humans are causing most of the warming.”
The Energy Balance
Scientists have calculated Earth’s energy balance, tracking the energy that comes in and goes out, said Stanford University climate scientist Noah Diffenbaugh.
They have measured the heat coming into Earth’s system from different sources, relying on satellite data for the past 38 years and other, less direct measurements before then. Those sources include the sun and natural changes in the sun’s energy, and volcanic eruptions that bring heat from the Earth’s crust. Human sources include greenhouse gases, air pollution like soot, and changes in land use that release and absorb carbon.
The natural components put together have changed global temperatures — but only a tiny amount. They account for between two-tenths of a degree of cooling and two-tenths of a degree of warming, the 2017 national science report said.
The national science report concluded that humans caused at least 93 percent of the warming that scientists measured from 1951 to 2010.
None of the natural effects could have possibly produced the warming that has been seen, they said. But “if you include effect of greenhouse gases, everything matches up,” said University of Illinois climate scientist Donald Wuebbles, one of the chief authors of the 2017 report.
The Way the Earth Warms
The world has warmed in exactly the way physics has predicted, what Oppenhiemer calls the “Cadillac piece of evidence.”
In a world warmed by greenhouse gases, physicists predicted that the air about 6 miles (10 kilometers) up would cool. And it has , Oppenheimer said. Had the warming been from the changes in the sun’s energy, that upper air wouldn’t cool.
Climate change theory also predicted that the poles would warm faster than the rest of the Earth. That too has happened, said Columbia University climate scientist Adam Sobel.
Another fingerprint that implicates human activity: The world’s much warmer oceans , Sobel said.
The greenhouse effect is no mystery. It was demonstrated nearly two centuries ago. Engineers have harnessed its effects — it helped the U.S. Air Force develop heat-seeking missiles. And it makes Earth livable.
It’s simply that certain gasses, including carbon dioxide and water vapor, trap heat.
Without it, much more of the sun’s heat would evaporate into space — Earth’s average temperature would be about -1 degrees (-18 Celsius). With the greenhouse effect it is a comfortable 59 degrees (15 Celsius).
Will it Change Back?
The Earth’s climate could “change back again,” as President Trump suggested — if humans drastically and permanently cut back emissions of greenhouse emissions. The problem is, Trump is taking steps that will increase emissions, such as from burning more coal, not decrease them.
With Trump’s moves, changes in climate will not be reversed, they will intensify.
Kathie Dello, a climate scientist at Oregon State University, calls Trump’s misinformation ‘dangerous.’
“It’s like jumping off a cliff and hoping that gravity just doesn’t exist anymore,” she said. “That’s what we’re doing by denying the basic science behind climate change.”