A coalition of prominent scientists, corporate leaders, and policymakers released a statement in the multidisciplinary scientific journal 'Nature', issuing a dire warning. They said that humanity may only have three years to vastly limit global emissions or it may be hopeless to keep climate change under control and within its safe limits.

Who is this group?

This group is being led by Costa Rican diplomat and former United Nations (UN) Climate Chief Christiana Figueres. She is also the person who oversaw the UN negotiations that produced the Paris Climate Agreement, which only three countries have rejected (America, Syria, Nicaragua).

Besides Figueres, the statement has five other authors and also has dozens of co-signers that includes other scientists, corporate leaders, and policymakers.

What is the math behind their reasoning?

The group says the statement they put out is founded on basic math. They concluded that the Earth has at most 600 billion tons of carbon dioxide (CO2) that can be released if humanity wants a solid chance at keeping the increase in global temperatures within 2.7 to 3.6 degrees Fahrenheit. There are around 41 billion tons of CO2 emitted every year, giving about 15 years before that amount of 600 billion would be reached.

What would have to happen to stay within the safe limits?

Obviously, global carbon dioxide emissions can't go from 41 billion to zero in only 15 years, since the global economy would come to a standstill.

Therefore the group behind this warning is saying that they must be put on a downward path right now. The group has set 2020 as the latest this can start because delaying it beyond that will not give the global economy enough time to transform. If emissions do not decline significantly by 2020, then the group warns that it will become progressively more difficult to control climate change.

This is because taking longer to act would mean a more rapid decline that would be needed to end CO2 emissions (see Carbon Crunch chart below). As the group's statement mentions at a certain point, it would be impossible to cut CO2 emissions as quickly as needed without tearing open the limited carbon "budget."

The group says that to meet the necessary decline by 2020 all power plants on Earth would have to be on the path to retirement, with no new ones being built.

Electric vehicles would have to go from 1% of global sales to 15%. Global deforestation would also have to quickly decline and then stop entirely, with the goal being for forests around the world to start pulling CO2 out of the atmosphere by 2030.