CNN summarizes the latest data, and the new confidence of scientists in their climate models.
First, the Earth has gotten warmer. Since 1850, average global temperatures have risen about .6 degrees Celsius, the United Nations says. Greenhouse gases such as carbon dioxide released by humans burning fossil fuels and clearing land are the likely culprits. Sea levels have also risen about 4 to 8 inches during the past century, according to the EPA.
Second, the concentration of greenhouse gases (or GHG) in the atmosphere is near its highest point in recorded history. Since the Industrial Revolution, concentrations of carbon dioxide, a potent greenhouse gas, have risen 30 percent.
In spite of the progress of the past 2 decades, a small number of scientists still think that the models are too unreliable. But they are in the “extreme minority”.
Despite the uncertainties, says Drew Shindell, a NASA climate modeler, […] climate models, at least in the short term, are good and “getting better.”
“The results become steadily less reliable as you go out in time,” Shindell said. “We can do a pretty good job 25 to 30 years out; we have a rough idea 50 years out. By the time you get into 100 years, there’s a lot of things we can’t really say.”
But Shindell says dozens of climate models run by scientists around the world convincingly describe a world sweating under the influence of greenhouse gases which trap the sun’s energy.
“There is no doubt that humans are warming the planet. That’s very clear now,” says Jeffrey Severinghaus, a geoscience researcher at the Scripps Institute of Oceanography. “The data is beautiful. It’s very strong. Humans are changing the climate, and we’re expected to change it a lot more in the future.”