It’s simple math really. A benchmark. A magic number that must never be reached. Two degrees Celsius. If you know anything about the global climate talks in Paris, you know that a central goal of the summit is to reach an agreement that would prevent global temperatures from rising two degrees or more above pre-industrial levels.
But why is this number different from all other numbers? In some ways, it’s not.
“Nature did not draw a line and say “Thou shalt not cross two degrees,” said Richard Alley, a geoscientist and climate historian at Pennsylvania State University. “The two-degree limit is not the end of life.”
But crossing two degrees, many scientists say, would provide a grim picture of our addiction to greenhouse gases. Akin to an unhealthy diet driving the progression to diabetes, two degrees symbolizes a dive into an unsustainable future.
The basic science is simple, said Columbia University economist Scott Barrett.
“To stabilize the climate, the concentration of these gases in the atmosphere have to be stable, and for them to be stable, given that some of these gases will last thousands of years, emissions have to go to zero,” he said. Failing to do so will alter the course of human society, not only down the road, but within the next few decades.
Imagine a Syrian refugee crisis happening every year, but magnified. Even if aggressive deals are reached in Paris over this week and next, climate change could still be on track to drive millions from their homes through drought, famine, sea-level rise and extreme storms like cyclones. Since 2008, 22.5 million have been displaced each year because of extreme weather, according to a report issued last week by the U.N. refugee agency. Warmer temperatures would be a boon for lethal diseases, like Ebola, bird flu and chikungunya, by allowing them to migrate into new habitats. The World Health Organization predicts that in just 15 years, climate change will kill 250,000 additional people per year through malnutrition, malaria, diarrhea and heat stress. Global warming could be this century’s World War, except festering over decades.
“This is probably the biggest, most-complicated, most long-term problem that we’ve ever dealt with,” said Princeton University geoscientist Michael Oppenheimer, a coordinating lead author of the latest United Nations Intergovernmental Panel on Climate Change report. “We know from human experience in the last 40, 50, 100 years that just natural climate changes present huge problems for humans.”
Not everyone buys into the perils of climate change. A poll from NPR and the Pew Research Center shows 30 percent of Americans and 40 percent globally aren’t convinced that climate change will personally hurt them. On Tuesday, The House of Representatives moved to block plans to cut greenhouse gases from U.S. power plants.
So how did we come to fear this global warming speed limit?
The two faces of 2°C global warming
The European Union officially proposed the 2 degree Celsius threshold in 1996, but its birth as a policy benchmark came nearly a decade earlier. The originators weren’t members of the Intergovernmental Panel on Climate Change, whose reports guide current-thinking on climate change, but rather the idea came from its predecessor, the Advisory Group on Greenhouse Gases. In late 1987, this group hosted two pioneering workshops — held in Villach, Austria and Bellagio, Italy — that examined more than a century of research into manmade greenhouse gas emissions.
It was in 1859 when Irish physicist John Tyndall discovered that some gases blocked infrared radiation and kept the planet warm. That’s now known as the greenhouse effect. At the time, the mean global temperature was 13.6 degrees Celsius, or 56.48 degrees Fahrenheit, and the Industrial Revolution was in full-swing.
The first true measurement of global warming came in 1896, when Swedish chemist Svante Arrhenius published research showing that “the temperature of the Arctic regions would rise about 8 degrees or 9 degrees Celsius, if the carbonic acid increased 2.5 to 3 times its present value.” English engineer Guy Stewart Callendar followed this work in 1938 by serendipitously predicting that a doubling of carbon dioxide in the atmosphere could elevate global temperatures by 2 degrees Celsius.
Decades flew by, modernity arrived, and climate models reinforced these early predictions suggesting that a doubling of carbon dioxide from pre-industrial levels — 280 parts per million — will likely increase global temperatures by 1.5 to 4.5 degrees Celsius, or 2.7 to 8.1 degrees Fahrenheit.
If nothing changes, the world will break the 2 degree Celsius barrier by mid-century, but on its own, the number is fairly arbitrary, some say.
“There’s nothing particularly special about the 2 degree target. But the more the mean temperature rises, the more you’re moving away from a system that we’ve been comfortable with and that has been stable for 10,000 years,” Barrett said. “It’s the things that would be triggered by the change in temperature that matter. There could be major changes in temperature and precipitation that would make parts of the world eventually uninhabitable by humans unless they were really dramatic forms of adaptation taken.”
One immediate effect on humans could be famine. Crop yields decline at a certain temperature threshold, and unless we can repeat the green revolution and make completely new crop varieties, the yields are going to decrease faster than our ability to cope, Oppenheimer said. Extreme weather like hurricanes and droughts would exacerbate our discomfort.
“If you look at the heat wave numbers, the changes in extreme heat are radical and fast. By the time you get to 2 degrees, you’re living in a much hotter and different world,” Oppenheimer said.
You also have a planet teetering toward permanent instability.
“When you get to around 2 degrees, the risks of part, one or both of the major ice sheets in Greenland and in Antarctica breaking up and coming loose start to rise markedly,” Oppenheimer said.
Two massive sheets of ice exist on Earth: The Greenland ice sheet, which contains an equivalent of about 23 feet of sea level rise, if all melted, and the Antarctic ice sheet, which contains about 187 feet of sea level rise. Most of that ice won’t melt unless the world warms by double digits, which is unlikely to occur, Oppenheimer said.
“Unfortunately, something on the order of five or 10 meters of sea level rise can be wrung out of Antarctica relatively quickly…over the course of a couple of hundred years and on a longer time scale, maybe seven meters from Greenland,” Oppenheimer said.
That’s about 40 feet when added together, he said — too much sea level rise for humanity to face.
“When we look at U.S. places hardest hit in the next few decades: there’s South Florida, where the bedrock is full of holes like Swiss cheese, so you can’t build sea walls. Norfolk, Virginia because of so many channels and rivers, and also the land is sinking. New York City and New Orleans too,” said Benjamin Strauss of Climate Central. “Abroad, East Asia will have some of the largest sea-level increments in the long-term. Many of those cities are sinking because they’re on deltas where sediment supply has decreased. The gravest problems will be in global megacities.”
Sea-level rise prediction for New York City via Climate Central
Sea-level rise prediction for Shanghai via Climate Central
There has been recent dispute over whether Antarctica is suffering from cataclysmic melting, especially in light of a NASA study last month that claimed the continent has gained, not lost ice since 1992. But other studies show that Antarctica’s western glaciers in the Amundsen sea are losing mass, and if they fail, could add 10 feet of water to the ocean. According to Washington Post’s Chris Mooney, scientists say the pledges made at the Paris talks won’t save the planet’s ice.
“Much of sea-level rise could come at a rate that humanity has never seen before, and it’s to avoid that instability and relatively sudden increase in sea level rise that the 2 degree target was originally conceived,” Oppenheimer said. “We do know that the last time Earth was about 2 degree Celsius warmer than preindustrial times, sea level was 5 to 10 meters [16 to 32 feet] higher than today. We’re not absolutely sure that that time in the past is a good analog for what’s happening in the future, but that’s not the kind of risk you want to take.”
Are we disarming a bomb that’s already gone off?
Barrett said the planet will inevitably surpass the 2 degree Celsius benchmark during this century, even with the calculations and intended pledges of the officials involved with the UN Convention on Climate Change and this week’s talks.
“These calculations show that even if countries fulfill their pledges, emissions will keep rising globally through 2030, and without any sign of stopping,” Barrett said. “And there’s no way you can meet any temperature target as long as emissions keep rising. The only way you can stabilize the climate is if global emissions head toward zero.”
Oppenheimer said the tipping point for reaching zero emissions greenhouse gases comes somewhere near the mid-century.
“The projections suggest that sometime after 2050 or 2060, but perhaps as late as 2100, we need to get close to zero emissions,” Oppenheimer said.
By then, humans need to have stopped emitting greenhouse gases, figured out how to sap these pollutants from the atmosphere or established some combination of the two.
The first option would require a massive shift to clean energy, and there are hints that this transition has started. A European report issued last week says the global growth of greenhouse gas emissions almost stalled in 2014. This shift was mainly due to China’s slow economic growth and switch to clean energy, though declining emissions in Europe, Japan and Australia helped too. The U.S. mirrored China in almost reaching stable levels.
Despite these achievements, emissions still grew and the planet still broke the world record for greenhouse gas concentrations in 2014, according to the The World Meteorological Organization. Renewable energy has made tremendous strides. Solar energy has boomed over the last decade, and wind energy has taken off in the United States, China, Europe and many other places around the world. On some days, Germany produces almost all its electricity with renewable energy.
Yet the U.S. Energy Information Administration (EIA) estimated in 2013 that only 11 percent of world’s marketed energy consumption came from renewable energy sources – biofuels, biomass, geothermal, hydropower, solar, and wind — and project that this value will only rise to 4 percent by 2040.
The prospects look grim for the second option of remediation: sucking carbon out of the sky. Carbon sequestration could, in theory, solve global warming. But the technology to date is too expensive and not ready for action on a global or regional scale, Oppenheimer said. Environmental reporter David Roberts takes things even further for Vox:
The mechanism for negative emissions is supposed to be bioenergy — burning plant mass — coupled with carbon capture and sequestration. The combo is called BECCS, and in theory, it buries more CO2 than it emits.
If you work enough BECCS into your model, you can almost double humanity’s “carbon budget” — the amount of carbon we can still pump in the atmosphere without passing 2°C. After all, if you can suck half the carbon out, you can afford to pump twice the carbon in.
But is large-scale BECCS plausible? There’s the problem of finding a source of biomass that doesn’t compete with food crops, the harvesting of which does not spur additional emissions, and which can be found in the enormous quantities required. The IPCC scenarios that come in below 2°C require BECCS to remove between 2 and 10 gigatons of CO2 a year from the atmosphere by 2050. By way of comparison, all the world’s oceans combined absorb about 9 gigatons a year; all the world’s terrestrial carbon sinks combined absorb about 10 gigatons a year.
That’s daunting given that the technology isn’t available. Investment in these innovations may be the champion of this week’s deliberations. On Monday, Bill Gates, Mark Zuckerberg and other business entrepreneurs announced a new fund to boost private sector interests in clean energy technology. A sister program recruited 20 nations to promise $20 billion for similar projects in the public sector. And on Tuesday, France pledged 2 billion euros over the next four years to African countries to develop in renewable energy sources.
Shutting off lights when you leave a room, switching to solar or driving a hybrid can help the cause. But cutting the emissions to zero would require an international commitment on par with the World Wars. Unlike the Kyoto agreement, the Paris talks are non-binding from a legal perspective.
“I think countries will come to an agreement in Paris because the obligations are based on voluntary pledges,” Barrett said. “It’s easy to agree to something when you know you’re not really going to be held accountable. And it’s somewhat I think deceptive to think that this is a success.”
But even binding agreements, like Kyoto, have failed to stop emissions in many nations. Plus, three of the biggest perpetrators — the U.S., China and India — wouldn’t ratify or wouldn’t agree to binding emissions targets with the Kyoto protocol.
Oppenheimer compares the situation to the threat of nuclear annihilation in 1950s and 1960s, which never came to fruition because of international diplomacy.
“We haven’t completely put the [nuclear weapon] genie back in the bottle, but cooler heads prevailed in countries that found a way to see their mutual interest in not annihilating each other,” Oppenheimer said.
But oddly, the atomic bomb provides a historical example of the type of innovation needed to save the planet from greenhouse gases. The Manhattan Project took five decades of atomic research and created a weapon in just four years that quite literally shook the world. The globe would see a tidal shift — either in renewable energy or carbon capture — on par with the scale of the atomic bomb to rectify our current situation.
That could happen with a major investment in renewable and carbon capture technology, Oppenheimer said, adding that he remains hopeful, despite the challenges:
As a whole, I think humans will in their own messy way start dealing with the problem. We throw up lots of obstacles for ourselves, create lots of mess, and then we clean up after ourselves. Climate change is like that. Some of the clean up is ugly and some of the mess really doesn’t go away, but my expectation is if you look back a century from now on what happened, we’ll probably say this is the period of time where we actually got seriously started, and we averted the worst kinds of outcomes.