“Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future,” Revelle and Suess wrote in the paper. It’s one of the most famous sentences in earth science history.
Here was the insight underlying modern climate science: Atmospheric carbon dioxide is increasing, and humans are causing the buildup. Revelle and Suess became the final piece in a puzzle dating back to Svante Arrhenius and John Tyndall. “I tell my students that to understand the basics of climate change, you need to have the cutting-edge science of the 1860s, the cutting-edge math of the 1890s and the cutting-edge chemistry of the 1950s,” says Joshua Howe, an environmental historian at Reed College in Portland, Ore.
Observational data collected throughout the second half of the 20th century helped researchers gradually build their understanding of how human activities were transforming the planet.
Ice cores pulled from ice sheets, such as that atop Greenland, offer some of the most telling insights for understanding past climate change. Each year, snow falls atop the ice and compresses into a fresh layer of ice representing climate conditions at the time it formed. The abundance of certain forms, or isotopes, of oxygen and hydrogen in the ice allows scientists to calculate the temperature at which it formed, and air bubbles trapped within the ice reveal how much carbon dioxide and other greenhouse gases were in the atmosphere at that time. So drilling down into an ice sheet is like reading the pages of a history book that go back in time the deeper you go.
using ice cores drilled at a U.S. military base in northwest Greenland. Contrary to expectations that past climates were stable, the cores hinted that abrupt climate shifts had happened over the last 100,000 years. By 1979, an international group of researchers was pulling another deep ice core from a second location in Greenland — and it, too, showed that abrupt climate change had occurred in the past. In the late 1980s and early 1990s, a pair of European- and U.S.-led drilling projects retrieved even deeper cores from near the top of the ice sheet, pushing the record of past temperatures back a quarter of a million years.
Together with other sources of information, such as sediment cores drilled from the seafloor and molecules preserved in ancient rocks, the ice cores allowed scientists to reconstruct past temperature changes in extraordinary detail. Many of those changes happened alarmingly fast. For instance, the climate in Greenland
warmed abruptly more than 20 times in the last 80,000 years, with the changes occurring in a matter of decades. More recently, a cold spell that set in around 13,000 years ago suddenly came to an end around 11,500 years ago — and temperatures in Greenland rose 10 degrees C in a decade.
Evidence for such dramatic climate shifts laid to rest any lingering ideas that global climate change would be slow and unlikely to occur on a timescale that humans should worry about. “It’s an important reminder of how ‘tippy’ things can be,” says Jessica Tierney, a paleoclimatologist at the University of Arizona in Tucson.
More evidence of global change came from Earth-observing satellites, which brought a new planet-wide perspective on global warming beginning in the 1960s. From their viewpoint in the sky, satellites have measured the rise in global sea level — currently 3.4 millimeters per year and accelerating, as warming water expands and as ice sheets melt — as well as the rapid decline in ice left floating on the Arctic Ocean each summer at the end of the melt season. Gravity-sensing satellites have “weighed” the Antarctic and Greenlandic ice sheets from above since 2002, reporting that more than 400 billion metric tons of ice are lost each year.
Temperature observations taken at weather stations around the world also confirm that we are living in the hottest years on record. The
10 warmest years since record keeping began in 1880 have all occurred since 2005. And nine of those 10 have come since 2010.
VIDEO Arctic sea ice cover, which dips to its annual minimum in September, has declined in recent decades. In 1979, the minimum extent was 6.90 million square kilometers. By 2021, it had dropped to 4.72 million square kilometers. Worrisome predictions
By the 1960s, there was no denying that the planet was warming. But understanding the consequences of those changes — including the threat to human health and well-being — would require more than observational data. Looking to the future depended on computer simulations: complex calculations of how energy flows through the planetary system.
A first step in building such climate models was to connect everyday observations of weather to the concept of forecasting future climate. During World War I, British mathematician Lewis Fry Richardson imagined tens of thousands of meteorologists, each calculating conditions for a small part of the atmosphere but collectively piecing together a global forecast.
But it wasn’t until after World War II that computational power turned Richardson’s dream into reality. In the wake of the Allied victory, which relied on accurate weather forecasts for everything from planning D-Day to figuring out when and where to drop the atomic bombs, leading U.S. mathematicians acquired funding from the federal government to improve predictions. In 1950, a team led by Jule Charney, a meteorologist at the Institute for Advanced Study in Princeton, N.J., used the ENIAC, the first U.S. programmable, electronic computer, to produce
the first computer-driven regional weather forecast. The forecasting was slow and rudimentary, but it built on Richardson’s ideas of dividing the atmosphere into squares, or cells, and computing the weather for each of those. The work set the stage for decades of climate modeling to follow.
By 1956, Norman Phillips, a member of Charney’s team, had produced the world’s first general circulation model, which captured how energy flows between the oceans, atmosphere and land. The field of climate modeling was born.
The work was basic at first because early computers simply didn’t have much computational power to simulate all aspects of the planetary system.
An important breakthrough came in 1967, when meteorologists Syukuro Manabe and Richard Wetherald — both at the Geophysical Fluid Dynamics Laboratory in Princeton, a lab born from Charney’s group — published a paper in the
Journal of the Atmospheric Sciences that modeled connections between Earth’s surface and atmosphere and calculated how changes in CO 2 would affect the planet’s temperature. Manabe and Wetherald were the first to build a computer model that captured the relevant processes that drive climate, and to accurately simulate how the Earth responds to those processes.
The rise of climate modeling allowed scientists to more accurately envision the impacts of global warming. In 1979, Charney and other experts met in Woods Hole, Mass., to try to put together a scientific consensus on what increasing levels of CO
2 would mean for the planet. The resulting “Charney report” concluded that rising CO 2 in the atmosphere would lead to additional and significant climate change.
In the decades since,
climate modeling has gotten increasingly sophisticated. And as climate science firmed up, climate change became a political issue. Backlash
The rising public awareness of climate change, and battles over what to do about it, emerged alongside awareness of other environmental issues in the 1960s and ’70s. Rachel Carson’s 1962 book
Silent Spring, which condemned the pesticide DDT for its ecological impacts, catalyzed environmental activism in the United States and led to the first Earth Day in 1970.
In 1974, scientists discovered another major global environmental threat — the Antarctic ozone hole, which had some important parallels to and differences from the climate change story. Chemists Mario Molina and F. Sherwood Rowland, of the University of California, Irvine, reported that chlorofluorocarbon chemicals, used in products such as spray cans and refrigerants, caused a chain of reactions that
gnawed away at the atmosphere’s protective ozone layer. The resulting ozone hole, which forms over Antarctica every spring, allows more ultraviolet radiation from the sun to make it through Earth’s atmosphere and reach the surface, where it can cause skin cancer and eye damage.
Governments worked under the auspices of the United Nations to craft the 1987 Montreal Protocol,
which strictly limited the manufacture of chlorofluorocarbons. In the years following, the ozone hole began to heal. But fighting climate change is proving to be far more challenging. Transforming entire energy sectors to reduce or eliminate carbon emissions is much more difficult than replacing a set of industrial chemicals.
In 1980, though, researchers took an important step toward banding together to synthesize the scientific understanding of climate change and bring it to the attention of international policy makers. It started at a small scientific conference in Villach, Austria, on the seriousness of climate change. On the train ride home from the meeting, Swedish meteorologist Bert Bolin talked with other participants about how a broader, deeper and more international analysis was needed. In 1988, a United Nations body called the Intergovernmental Panel on Climate Change, the IPCC, was born. Bolin was its first chairperson.
The IPCC became a highly influential and unique body. It performs no original scientific research; instead, it synthesizes and summarizes the vast literature of climate science for policy makers to consider — primarily through massive reports issued every couple of years.
The first IPCC report, in 1990, predicted that the planet’s global mean temperature would rise more quickly in the following century than at any point in the last 10,000 years, due to increasing greenhouse gases in the atmosphere.
IPCC reports have played a key role in providing scientific information for nations discussing how to stabilize greenhouse gas concentrations. This process started with the
Rio Earth Summit in 1992, which resulted in the U.N. Framework Convention on Climate Change. Annual U.N. meetings to tackle climate change led to the first international commitments to reduce emissions, the Kyoto Protocol of 1997. Under it, developed countries committed to reduce emissions of CO 2 and other greenhouse gases. By 2007, the IPCC declared the reality of climate warming is “unequivocal.” The group received the Nobel Peace Prize that year, along with Al Gore, for their work on climate change.
The IPCC process ensured that policy makers had the best science at hand when they came to the table to discuss cutting emissions. Of course, nations did not have to abide by that science — and they often didn’t. Throughout the 2000s and 2010s, international climate meetings discussed less hard-core science and more issues of equity. Countries such as China and India pointed out that they needed energy to develop their economies and that nations responsible for the bulk of emissions through history, such as the United States, needed to lead the way in cutting greenhouse gases.
Meanwhile, residents of some of the most vulnerable nations, such as low-lying islands that are threatened by sea level rise, gained visibility and clout at international negotiating forums. “The issues around equity have always been very uniquely challenging in this collective action problem,” says Rachel Cleetus, a climate policy expert with the Union of Concerned Scientists in Cambridge, Mass.
By 2015, the world’s nations had made some progress on the emissions cuts laid out in the Kyoto Protocol, but it was still not enough to achieve substantial global reductions. That year, a key U.N. climate conference in Paris produced an international agreement to try to
limit global warming to 2 degrees C, and preferably 1.5 degrees C, above preindustrial levels.
Every country has its own approach to the challenge of addressing climate change. In the United States, which gets approximately 80 percent of its energy from fossil fuels, sophisticated efforts to downplay and critique the science led to major delays in climate action. For decades, U.S. fossil fuel companies such as ExxonMobil worked to influence politicians to take as little action on emissions reductions as possible.
Such tactics undoubtedly succeeded in feeding politicians’ delay on climate action in the United States, most of it from Republicans. President George W. Bush
withdrew the country from the Kyoto Protocol in 2001; Donald Trump similarly rejected the Paris accord in 2017. As late as 2015, the chair of the Senate’s environment committee, James Inhofe of Oklahoma, brought a snowball into Congress on a cold winter’s day to argue that human-caused global warming is a “hoax.”
In Australia, a similar mix of right-wing denialism and fossil fuel interests has kept climate change commitments in flux, as prime ministers are voted in and out over fierce debates about how the nation should act on climate.
Yet other nations have moved forward. Some European countries such as Germany aggressively pursued renewable energies, including wind and solar, while activists such as Swedish teenager Greta Thunberg —
the vanguard of a youth-action movement — pressured their governments for more.
In recent years, the developing economies of China and India have taken center stage in discussions about climate action. China, which is now the world’s largest carbon emitter, declared several moderate steps in 2021 to reduce emissions, including that it would stop building coal-burning power plants overseas. India announced it would aim for net-zero emissions by 2070, the first time it has set a date for this goal.
Yet such pledges continue to be criticized. At the 2021 U.N. Climate Change Conference in Glasgow, Scotland, India was globally criticized for not committing to a complete phaseout of coal — although the two top emitters, China and the United States, have not themselves committed to phasing out coal. “There is no equity in this,” says Aayushi Awasthy, an energy economist at the University of East Anglia in England.
Facing the future
In many cases, changes are coming faster than scientists had envisioned a few decades ago. The oceans are becoming more acidic as they absorb CO
2, harming tiny marine organisms that build protective calcium carbonate shells and are the base of the marine food web. Warmer waters are bleaching coral reefs. Higher temperatures are driving animal and plant species into areas in which they previously did not live, increasing the risk of extinction for many.
No place on the planet is unaffected. In many areas, higher temperatures have led to major droughts, which dry out vegetation and provide additional fuel for
wildfires such as those that have devastated Australia, the Mediterranean and western North America in recent years.
Then there’s the Arctic, where temperatures are rising at more than twice the global average and communities are at the forefront of change. Permafrost is thawing, destabilizing buildings, pipelines and roads. Caribou and reindeer herders worry about the increased risk of parasites for the health of their animals. With less sea ice available to buffer the coast from storm erosion,
the Inupiat village of Shishmaref, Alaska, risks crumbling into the sea. It will need to move from its sand-barrier island to the mainland.
“We know these changes are happening and that the Titanic is sinking,” says Louise Farquharson, a geomorphologist at the University of Alaska Fairbanks who monitors permafrost and coastal change around Alaska. All around the planet, those who depend on intact ecosystems for their survival face the greatest threat from climate change. And those with the least resources to adapt to climate change are the ones who feel it first.
“We are going to warm,” says Claudia Tebaldi, a climate scientist at Lawrence Berkeley National Laboratory in California. “There is no question about it. The only thing that we can hope to do is to warm a little more slowly.”
That’s one reason why
the IPCC report released in 2021 focuses on anticipated levels of global warming. There is a big difference between the planet warming 1.5 degrees versus 2 degrees or 2.5 degrees. Each fraction of a degree of warming increases the risk of extreme events such as heat waves and heavy rains, leading to greater global devastation.
The future rests on how much nations are willing to commit to cutting emissions and whether they will stick to those commitments. It’s a geopolitical balancing act the likes of which the world has never seen.