Over the last 130 years, global temperatures have risen 1.4 ˚F, and the weight of scientific evidence confirms that human activities are to blame. Most climate scientists agree that if we want to halt rising temperatures, the onus is on us. Two recent studies solidify that conclusion.
The first looks at something that has been hypothesized as a driver of climate change—cosmic rays from the sun. It’s a frequent argument put forth by climate change deniers as an alternative to greenhouse gas pollution. To test the hypothesis, two British scientists, Terry Sloan at the University of Lancaster and Sir Arnold Wolfendale at the University of Durham, compared data on cosmic rays and global temperatures from 1955 to the present. Here’s Paul Brown, writing at Scientific American:
By comparing the small oscillations in cosmic ray rate and temperature with the overall trends in both since 1955, Sloan and Wolfendale found that less than 14 percent of the global warming seen during this period could have been caused by solar activity.
After comparing the results of this study with their previous efforts and those of others, they concluded that less than 10% of the warming in the 20th century was attributable to changes in the sun’s output.
The focus of the other study are chlorofluorocarbons, known as CFCs, which are known to cause climate change. Fortunately, they don’t appear to be as much of a culprit these days, and that could be due to an international treaty signed in the late 1980s. Now tightly restricted in many countries, CFCs are harmful to the ozone layer and are potent greenhouse gases, with hundreds to thousands of times the warming power of CO2. It also happens that in the last 15 years, global warming has gone on hiatus, a fact which piqued the interest of Francisco Estrada, an ecological economist at the Free University in Amsterdam, and his research team.
Hannah Hoag, reporting for Nature News:
Estrada’s study links that to the 1987 Montreal Protocol that banned the release of CFCs — once used widely in refrigerants, solvents and propellants — to stop ozone depletion, which allowed more warming solar radiation to reach Earth. Temperatures today might have been 0.1 °C warmer had CFC emissions continued unabated, according to a commentary to be published alongside the study.
The study doesn’t include enough data to directly link the drop in CFCs with the pause in warming, but it is suggestive of the impact of international agreements.