In 2002-2003 the world produced about 44 gigatons of CO2e (Carbon Dioxide equivalent) gasses per year. Fast forward 10 years and the latest UNEP report shows that in 2012, we emitted about 50 GT, a whopping 13.6 percent increase, and this despite a major economic recession.


This is a big, big problem.


44 GT, as it turns out, is the magic number we need to achieve by 2020 to avoid catastrophic climate change, which is defined as a greater than 2 degree Celsius rise in global temperatures over pre-industrial levels. But looking at the current trajectory of growth of carbon emissions, if we were to do nothing and let business proceed as usual, we could hit 58 GT or more of CO2e emissions per year by 2020, leading to a 3-degree, 4-degree or even a 5-degree trajectory.


I should mention that the record-breaking year we just experienced here in the U.S. — a year of heat waves, drought, forest fires, flooding, and let's not forget Superstorm Sandy — came as a result of just 1-degree C temperature rise. A 2-degree world would not be just double the number of extreme weather events like Sandy, it would mean exponentially greater and more varied impacts. And as the Arctic permafrost melts, it would release vast stores of methane, a gas 25 times more powerful than CO2. This would lock in runaway climate change, transforming the very fabric of life on Earth.


Virtually all of the world’s governments have agreed that we need to keep global temperature rise below 2 degrees C compared to pre-industrial levels. So beginning in 2010, the United Nations has commissioned annual research to estimate the 2020 "emissions gap" — the gap between the emissions reductions needed to avoid irreversible impacts of climate change and the reductions pledged by world governments in the COP ("Conference of Parties") climate talks.


Next week, the 18th such conference begins, and with these latest findings, one can hope that governments including the U.S. (which has historically been a significant blocker in the climate talks) will see this looming eight-year horizon and get scared enough to increase their ambition for an effective climate treaty.


Currently, world governments participating in the U.N. COP, are pledging to reduce emissions in the ballpark of 3-4 GT by 2020. But based on the math, we need reductions on the order of 14 GT. In other words, we're not even close. By 2050, we need to be at 20 GT, and by 2100 down to 10 GT. 


This is why a slew of reports have been issued, including this dire report by the World Bank, warning that we're on track for 4 degree C temperature rise by the end of the century if nothing is done. It's quite hard to imagine what that world would look like, but the World Bank, an organization not typically known for hyperbole, describes the consequences in near apocalyptic terms.


There is some good news. The UNEP report, led by 43 science teams in 22 countries, demonstrates that we can solve this problem using existing technologies and commonsense efficiency regulations. For example, short-term investments in the energy efficiency of buildings can return 2 GT in CO2 cuts by 2020, and 9 GT in cuts by 2050. Investing in public transportation, fuel efficiency measures, and land planning that encourages cycling and walking can return another 2 GT. Largely underutilized policies that protect forests — which act as carbon sinks — are low-cost ways to avoid 2 GT or more of further greenhouse gas emissions. Ramping up clean renewable sources of energy could contribute another 2-4 GT in savings. 


So it's not a technological problem we face; it's a political problem. It's time we start demanding that our leaders step up to the challenge, put their partisan bickering aside, and get to work on the biggest challenge our civilization has ever faced.


44 gigatons: The most important number in the world
A new U.N. report challenges the world with a daunting task — reduce greenhouse gas emissions to 44 GT by 2020 or hit the tipping point for catastrophic clima