How Can Global CO2 Levels Soar When Emissions Are Flat?

Haiti drought worsened by the El Nino. CREDIT: DIEU NALIO CHERY, AP
Haiti drought worsened by the El Nino. CREDIT: DIEU NALIO CHERY, AP

Last year saw the biggest jump in global CO2 levels ever measured, as NOAA reported on March 9. Yet in 2015 the world economy grew while energy-related CO2 emissions were flat — for the second year in a row — according to the International Energy Agency, as ClimateProgress reported last week.

This puzzled more than one reader. One emailed me the following: “the IEA is saying that emissions have gone flat, while, at the same time, NOAA is announcing that we just had the largest-ever jump in CO2 [levels]. Logic would seem to dictate that someone has their figures wrong. Flat emissions should not translate into record CO2 jumps.”

What’s going on? Two things:

  • Annual CO2 emissions are very different from global CO2 levels.
  • CO2 levels tend to have big jumps in El Niño years.

Let’s go through those two, especially since this discussion gets to the heart of what I call “the biggest source of confusion in the public climate discussion” in my recent book, “Climate Change: What Everyone Needs to Know.” It also goes to the heart of why delaying action is so dangerous and costly.

The CO2 Bathtub Analogy

Avoiding catastrophic warming requires stabilizing CO2 concentrations (or levels) in the atmosphere, not annual emissions. Studies find that many, if not most, people are confused about this, including highly informed people, mistakenly believing that if we stop increasing emissions, then global warming will stop. In fact, very deep reductions in greenhouse gas emissions are needed to stop global warming.

One study by MIT grad students found that “most subjects believe atmospheric GHG concentrations can be stabilized while emissions into the atmosphere continuously exceed the removal of GHGs from it.” The author, Dr. John Sterman from MIT’s Sloan School of Management, notes that these beliefs “support wait-and-see policies but violate conservation of matter” and are “analogous to arguing a bathtub filled faster than it drains will never overflow.”


While atmospheric concentrations (the total stock of CO2 already in the air) might be thought of as the water level in the bathtub, emissions (the yearly new flow into the air) are the rate of water flowing into a bathtub from the faucet. There is also a bathtub drain, which is analogous to the so-called carbon “sinks” such as the oceans and the soils. The water level won’t drop until the flow through the faucet is less than the flow through the drain.

Similarly, carbon dioxide levels won’t stabilize until human-caused emissions are so low that the carbon sinks can essentially absorb them all. Under many scenarios, that requires more than an 80 percent drop in CO2 emissions. And if the goal is stabilization of temperature near or below the 2°C (3.6 °F) threshold for dangerous climate change that scientists and governments have identified, then CO2 emissions need to approach zero by 2100.

So the first key point is that CO2 levels will continue rising if we merely keep annual CO2 emissions flat. In fact, they will keep rising at a faster and faster rate because the land and ocean carbon sinks are weakening (see below).

The Temporary Impact Of El Niño

NOAA reported two weeks ago that the CO2 concentrations “measured at NOAA’s Mauna Loa Observatory in Hawaii jumped by 3.05 parts per million during 2015, the largest year-to-year increase in 56 years of research.” That is a big jump compared to the average annual rise at Mauna Loa from 2005 to 2014 of 2.11 ppm per year.

But the second-highest single-year growth rate for CO2 levels was back in 1998, which saw a jump of 2.93 ppm (whereas the average annual rise from 1995 to 2004 was 1.87 ppm per year).

You may notice a pattern here — big jumps during big El Niño years.

“El Niño years tend to be bad years for plant growth, due to things like widespread drought or other extreme weather,” Stefan Rahmstorf, co-chair of Earth System Analysis at the Potsdam Institute for Climate Impact Research, explained in an email. “So the biosphere loses some carbon. You see that happening in 1998 as well. Below is a diagram from the AR5, you see from the squiggly line how variable the land sink is, it dominates interannual variability in the carbon budget.”

Annual manmade CO2 emissions and where they end up. The partitioning is between the ocean sink (dark blue), the atmosphere (light blue) and the land sink (green). CREDIT: IPCC
Annual manmade CO2 emissions and where they end up. The partitioning is between the ocean sink (dark blue), the atmosphere (light blue) and the land sink (green). CREDIT: IPCC

A crucial point is that, based on actual observations and measurements, the world’s top carbon cycle experts have determined that the land and oceans are becoming steadily less effective at removing excess CO2 from the atmosphere, as I reported last year. This makes it more urgent for us to start cutting carbon pollution ASAP, since it will become progressively harder and harder for us to do so effectively in the coming decades.

In particular, the defrosting permafrost and the resultant release of CO2 and methane turns part of the land sink into a source of airborne greenhouse gases. Similarly, as global warming increases forest and peatland fires — burning trees and vegetation — that also turns one part of the land carbon sink into a source of atmospheric CO2. So does ever-worsening droughts that scientists are observing in the United States southwest and other parts of the world.

We are destroying nature’s ability to help us stave off catastrophic climate change. “Clearly nature is helping us” deal with atmospheric CO2 right now much more than it will be decades to come, as Dr. Josep (Pep) Canadell, executive director of the Global Carbon Project, told me last year. Ultimately this is one more reason why delaying action to cut carbon pollution is a costly and dangerous mistake.