In discussions about reducing global climate change, the two degree Celsius threshold is often at its center. But why is it important, and how much difference can two degrees really make?

The 2°C threshold was set by the 2009 Copenhagen Accord, a document signed by 186 countries (including the United States) on the final day of the 2009 UN Climate Change Conference. The threshold itself had actually been agreed to by members of the G8 (the eight wealthiest countries on the planet) earlier that year. During that meeting, G8 leaders said they would cut their greenhouse gas emissions by 80 percent by 2050.

Hot Sun

Why cut greenhouse gas emissions? Because emissions of gases such as carbon and methane from industrial processes and automobiles remain in the Earth’s atmosphere and trap the heat from the sun, gradually warming the planet and causing a host of significant, negative impacts.

Therefore, the 2009 Copenhagen Accord was a promise by most of the world’s countries to reduce fossil fuel emissions and keep the average global temperature from rising by 2°C by the end of this century.

Unfortunately, countries have, for the most part, failed to do this. A recent report from the U.S. Environmental Protection Agency shows that the U.S. increased its emissions between 2012 and 2013. A report released this week from the European Union’s Joint Research Center shows that Brazil, India, China and Indonesia also increased their emissions this year. All told, 35.3 billion tons of carbon dioxide was pumped into the atmosphere last year.

Meanwhile, the G20 is paying $775 billion every year to subsidize the use and production of fossil fuels.

What’s Going on Right Now?

At this point, some effects of global warming are no longer negotiable. Glaciers in western Antarctica are in a state of “irreversible retreat,” according to NASA, and will help to raise sea levels throughout the coming centuries. Island nations like Kiribati are expected to disappear in the next three decades (Kiribati has already purchased land on another island in anticipation of moving its entire population) and so are portions of sea-level states like the southern points of Louisiana and Florida.

Severe droughts, such as the one in California that scientists have calculated as the worst in 1,200 years (and which has been exacerbated by climate change), are predicted to become much more common. Meanwhile, lethal heat waves, such as the ones that recently struck China and Australia, are also expected to grow in frequency and intensity.

How Much Damage Does a Degree Do?

The planet has already warmed up by 0.85 degrees C since about 1880.

“At one degree,” Professor Anders Levermann from the Potsdam Institute for Climate Change Research recently told Renew Economy, “we are already experiencing damages. Sea level rise in the long term…is somewhere in the vicinity of two meters. That puts cities like New York, Calcutta and Shanghai in difficult positions, and they need to protect themselves.”


Scientists use different models for calculating climate change. At the low, optimistic end, the planet warms less than two degrees by 2100. That’s if all nations dedicated themselves to eliminating fossil fuels and focusing on renewable energies. It’s not likely. But at the high, pessimistic end (if emissions continue to grow and grow), models show a warming of more than four degrees above pre-industrial levels by the end of the century.

That kind of rapid, intense temperature shift would be very bad, not only for crops and wildlife but also for national security. The U.S. Defense Department is so concerned with climate change driving global conflicts that they have listed it as a major threat to prepare for in the coming years.

How do just a few degrees cause such problems? Because that’s a global average, meaning some places will have much higher temperature increases and, because the carbon in the atmosphere causes natural weather systems to spazz out, some places will actually get much colder.

These changes are having effects that we can see today. This year, 2014, is on track to be the hottest year on record. (Update, January 2015: It was.)

Global average temperature from 1850 - 2012. The colored lines represent three different datasets. (Source: IPCC 5th Assessment Report)

Global average temperature from 1850 – 2012. The colored lines represent three different datasets. (Source: IPCC 5th Assessment Report)

Are We Going to Make It?

So how are the planet’s prospects for keeping global warming under two degrees Celsius?

“There was little scientific basis for the 2°C figure that was adopted,” David Victor, professor of international relations at UC San Diego, and his coauthor, Charles Kennel, director emeritus of the Scripps Institution of Oceanography, wrote in October,  “but it offered a simple focal point and was familiar from earlier discussions. […] At the time, the 2°C goal sounded bold and perhaps feasible.”

Unfortunately, these men say that the goal is now “effectively unachievable” and “impractical.”

But as Distinguished Professor of Meteorology Michael Mann told Planet Experts back in September, even if we miss the 2°C threshold, that doesn’t mean we should stop trying to reduce emissions.

“The actual situation is a little more nuanced than that,” he said, “in the sense that it’s less like a cliff that we walk off and more like a steeply descending slope. And we may miss the 450 ppm CO2 offramp on that highway. It doesn’t mean we give up. We still try to get off at the 460 ppm offramp, and if we miss that then we take the next one. With each of those junctures, however, there is a greater probability that we commit to some irreversible changes.”

So if the proverbial horse (and by horse, I mean carbon) throws us off, the best thing we can do is dust ourselves off, wipe the sweat out of our eyes, and try to break it in again.

Also, bear in mind that this is not a problem that can be solved by governments alone. Last month, Richard Heede published a report that linked just 90 companies to 63 percent of worldwide greenhouse gas emissions.

We need to change a lot more than our politics before we change the world.

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