“Climate Change is Now More Certain Than Ever,” New Report Says

by Shannon Hall on February 28, 2014

Image Credit: NASA

Melting sea ice is an iconic example of climate change. Image Credit: NASA

Climate change is one of the defining issues of our time. So begins the latest report by the U.S. National Academy of Sciences and the United Kingdom’s Royal Society. The two institutions agree: climate change is not only indisputable, it’s largely the result of human activities.

The bulk of the 36-page report is presented in a question-and-answer format, making it a good bed-side read. But in case you don’t want to have nightmares about surging temperatures or polar bears alone on breaking ice caps, we’ll leaf through the intriguing points here.

In a forward to the report, Dr. Ralph J. Cicerone, president of the National Academy of Sciences, and Sir Paul Nurse, president of the Royal Society argue that multiple lines of evidence show that humans are changing Earth’s climate. This is now more certain than ever.

They are careful to include a caveat: “The evidence is clear. However, due to the nature of science, not every single detail is ever totally settled or completely certain. Nor has every pertinent question yet been answered.” Areas of active debate include how much warming to expect in the future and the connections between climate change and extreme weather events such as the frequency and intensity of hurricanes, droughts and floods.

Earth’s global average surface temperature has risen as shown in this plot of combined land and ocean measurements from 1850 to 2012, derived from three independent analyses of the available data sets. The temperature changes are relative to the global average surface temperature of 1961?1990. Source: IPCC AR5, data from the HadCRUT4 dataset (black), UK Met Office Hadley Centre, the NCDC MLOST dataset (orange), US National Oceanic and Atmospheric Administration, and the NASA GISS dataset (blue), US National Aeronautics and Space Administration.

Earth’s global average surface temperature has risen as shown in this plot of combined land and ocean measurements from 1850 to 2012, derived from three independent analyses of the available data sets. Image Credit: National Academy of Sciences / The Royal Society

But the first question: is the climate warming? goes without debate. Yes. Earth’s average surface air temperature has increased by about 0.8 degrees Celsius since 1900, and the last 30 years have been the warmest in 800 years. It’s the most rapid period of sustained temperature change in the scale of global history, trumping every ice age cycle.

Recent estimates of the increase in global temperature since the end of the last ice age are four to five degrees Celsius. While this is much greater than the 0.8 degree Celsius change recorded over the last 100+ years, this change occurred over a period of about 7,000 years. So the change in rate is now 10 times faster.

Of course an increase in temperature goes hand in hand with an increase in carbon emissions. Greenhouse gases such as carbon dioxide absorb heat (infrared radiation) emitted from the Earth’s surface. Increases in the atmospheric concentrations of these gases trap most of the outgoing heat, causing the Earth to warm. Human activities, especially the burning of fossil fuels have increased carbon dioxide concentrations by 40 percent between 1880 and 2012. It is now higher than at any time in at least 800,000 years.

And if the rise in carbon emissions continues unchecked, warming of the same magnitude as the increase out of the last ice age can be expected by the end of this century.

The report continues to ask more controversial questions. Take as an example the question: Does the recent slowdown of warming mean that climate change is no longer happening? The short answer is no. Decades of slow warming and accelerated warming occur naturally in the climate system. Despite the slower rate of warming the 2000’s were still warmer than the 1990’s

The new report builds upon the long history of climate-related work from the United Nations’ Intergovernmental Panel on Climate Change. So while some have argued it doesn’t add anything new to the wealth of climate science data available, it does help make that data more succinct and available to the public. Its goal is to help inform decision makers, policy makers, educators and all other individuals.

The report concludes by noting available options to citizens and governments. They can simply wait and accept the losses, they can change their pattern of energy production, they can attempt to adapt to environmental changes as much as possible, or they can seek as yet unproven geoengineering solutions.

No matter which option we choose, one thing remains certain: the Earth is warming at a tremendous rate and we are the cause.

The paper is available for download here.


Shannon Hall is a freelance science journalist. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. Currently, she is working toward a second M.S. from NYU's Science, Health and Environmental Reporting program.

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