How come nations’ climate targets don’t compare?

This week’s climate change summit features lots of talk from different nations about their goals for reducing carbon emissions. But in the weird world of national climate pledges, numbers often aren’t quite what they seem.

Sometimes a 55% reduction is about equal to 50% to 52%. Sometimes it’s even less. Sometimes it’s way more.

As part of the Paris climate agreement process, each nation picks its own national goals for how much greenhouse gas should be cut by 2030 and — crucially — what baseline year it starts counting from for those cuts. That makes it difficult to compare countries’ emissions-cutting pledges to see who is promising more.

US AND EU GOALS

Both the United States and the European Union are offering similar-sounding pledges of cutting around half their emissions by 2030. But depending on what year you start from, each can sound significantly deeper than the other.

The European Union goal, newly approved by the union’s parliament, is 55% below 1990 levels. The new U.S. goal announced Thursday by President Joe Biden is 50% to 52% below 2005 levels.

If you convert the European goal to the American-preferred 2005 baseline, the two are the same. The European Union goal translates to 51% below 2005 levels, which is on par with the U.S. goal, said former Obama White House environmental aide Kate Larsen, a director at the private research Rhodium Group.

But if you compare them using Europe’s preferred 1990 as the baseline, the 50% minimum U.S. cut is only 41%, far shy of the 55% EU goal, according to Larsen’s calculations.

If you compare the numbers to 2019, the last pre-pandemic year, the U.S. goal looks more ambitious than Europe’s. The minimum the United States would be cutting is about 40% from today’s level and the EU only 35%, said Niklas Hohne, a climate scientist who helps run the Climate Action Tracker, which monitors world emission pledges.

WHY DIFFERENT BASELINES?

The idea behind different baselines goes back to a logjam that bogged down climate talks in 2009.

Developed countries that already spewed lots of carbon pollution wanted poorer nations that were counting on fossil fuels for economic development to forgo the dirtier fuels, said John Podesta, who was then-President Barack Obama’s climate czar. So a solution was struck for the 2015 Paris agreement that allowed nations to voluntarily choose their own goals tailored to each country.

Those nationally designed goals also included countries choosing their own baseline years. So countries tend to choose years in which they peaked or near peaked on carbon emissions.

For example, Europe, which took early action after the 1997 Kyoto Protocol, chose to keep that treaty’s 1990 baseline because it factored in early cuts. This way, Europe gets credit for acting early.

DOES IT MATTER?

Many developed nations’ goals pretty much even out, said Nigel Purvis, who was a U.S. State Department climate negotiator for the George W. Bush and Bill Clinton administrations.

“At 50%, they’re all doing a lot,” Purvis said. “The baselines are becoming less important.”

HIGHER GOALS

Some nations are shooting higher.

University of Maryland global sustainability professor Nate Hultman pointed to Denmark, which he said did the math to see how much emissions cutting was feasible for the future and found it to be 65% below 1990 levels. Denmark then purposely set a tougher goal, 70%, counting on unforeseen changes in technology that often happen.

Climate Action Tracker’s Hohne said that despite the White House’s claims, the U.S. target is not enough to keep warming to no more than 1.5 degrees Celsius since pre-industrial times, the tougher Paris agreement target.

The entire world must cut its emissions in half compared to 2019, Hohne said. But Biden’s new U.S. target only translates to about 40% from 2019 levels.

“If you take that comparison, then it doesn’t work,” Hohne told The Associated Press on Thursday.

NOT JUST CARBON DIOXIDE

Like other nations, the U.S. goal includes methane and hydrofluorocarbon gases that trap more heat but don’t last as long as carbon dioxide. Including those in the goals allows the United States to pick low-hanging fruit to better reach its goal, Larsen said.

Russian President Vladimir Putin emphasized how slashing methane pollution quickly can get the world nearly halfway to its 1.5 degree Celsius goal.

Reducing methane and HFCs gets results more quickly than cutting carbon dioxide, so cutting them “can buy us a lot of time,” Larsen said.

HOW TO REACH US GOAL

Most of the U.S. emissions reductions — about 70% — will likely come from the power sector, Hultman said. Switching to greener electricity would more quickly reduce overall emissions because people keep their cars for almost a dozen years.