How do scientists know for sure that global warming is man-made? – NBC 6 South Florida
Call it Law and Order: Climate Change. Scientists have used detective work to identify the main suspect of the Earth’s warming: us.
They proved that it could only be carbon dioxide and other greenhouse gases from burning fossil fuels.
For more than 30 years, the world’s top scientists have worked together for years to report on climate change and its causes and with each report – and rising global temperatures – they have become increasingly certain that climate change is caused by human activities. In the latest version of their report they said, “It is unequivocal that human influence has warmed the atmosphere, the ocean and the land.”
Scientists – including the late Ralph Cicerone, the former president of the National Academy of Scientists – have told The Associated Press that their confidence that climate change is a man-made problem equates to their certainty that they understand. that cigarettes are deadly.
One way to show that humans caused the warming “is to rule out everything else,” said Gabe Vecchi, a climatologist at Princeton University.
Scientists can calculate how much heat different suspects are trapping, using a complex understanding of chemistry and physics and feeding that into computer simulations that have been generally accurate in describing climate, past and future. They measure what they call radiative forcing in watts per square meter.
The first and most common natural suspect is the sun. The sun is what warms the Earth in general, providing about 1,361 watts per square meter of heat year after year. It is the baseline, the delicate balance that makes the Earth livable. Energy changes from the sun were minimal, about a tenth of a watt per square meter, the scientists calculate.
But carbon dioxide from burning fossil fuels now traps heat at the level of 2.07 watts per square meter, more than 20 times that of the sun’s changes, according to the US Environmental Protection Agency. Methane, another powerful heat-trapping gas, is at 0.5 watts per square meter.
The sun’s 11-year cycle has regular but small ups and downs, but that doesn’t seem to be changing Earth’s temperature. And if anything, the very slight changes in the 11-year average solar irradiance have moved down, according to NASA calculations, the space agency concluding “therefore it is extremely unlikely that the Sun has caused the warming trend in global temperature observed over the past century”.
Climate Central’s Climate Change Index shows the “fingerprints” of climate change – showing how its impacts, such as lingering heat overnight, can cause heat waves. Chase Cain, LX News climate storyteller, explains.
In other words, the sun had an alibi.
The other natural suspects – volcanoes and cosmic rays – have had even less influence over the past 150 years of warming, the scientists conclude.
The other way to show that carbon dioxide is causing the warming is to construct what Vecchi calls “a causal chain.”
National Oceanic and Atmospheric Administration records measured at a Hawaiian volcano show rising carbon dioxide levels, as do ice records that date back thousands of years. But the key is knowing what kind of carbon dioxide.
There are three types of materials containing carbon. Some contain light carbon, or carbon-12. Some contain heavy carbon or carbon 13 and still others contain radioactive carbon 14.
Over the past century or so, there has been more carbon-12 in the atmosphere than carbon-13, and less carbon-14 in recent decades, according to NOAA. Carbon-12 is essentially fossil carbon from long ago, as in fossil fuels. So the change in the ratio of carbon-12 to carbon-13 tells scientists that the carbon in the air comes more from burning fossil fuels than natural carbon, Vecchi said.
It is the fingerprint of the combustion of coal, oil and natural gas.
EDITOR’S NOTE: This story is part of an ongoing series that answers some of the most fundamental questions about climate change, the science behind it, the effects of global warming, and how the world faces it.
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