How can global CO2 levels soar when emissions are flat?

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Climate Progress

Haiti drought worsened by the El Nino.

Haiti drought worsened by the El Nino.

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

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.

Source: Climate Progress. Reproduced with permission.  

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  • neroden

    Basically, the CO2 was being absorbed in the ocean, and gets released during El Nino?

    • phred01

      also bush fires

  • trackdaze

    Keep in mind the latency (delayed effect) of co2 as a greenhouse gas. This is to say we won’t see the full effect of the current level for years. Or, inversely we`re only just seeing the early 2000`s effect on climate.

    Given that Co2 emmisions are still at near record levels its troubling to think what things may look like in 5-10short years.

    • juxx0r

      Can you explain the mechanism for the delay?

      • trackdaze

        Thermal inertia: most notably of the oceans.

  • Rasa

    At the start if the industrial revolution CO2 concentrations were approaching 1 part in 2,500 parts. Now, CO2 concentrations have exploded and are now …………..approaching 1 Part in 2,500. Devastating….. Apparently.

    • john
    • NiCuCo

      CO2 levels have increased more than 40% since the start of the Industrial Revolution.

      Carbon dioxide levels are now about 400 ppm. For over 400,000 years, CO2 levels have never been below 180 or above, until now, 300 ppm. Three hundred years ago they were 280 ppm. At its lowest, the Earth was about 10 C° colder than it is now, with about 180 ppm CO2, and glaciers covered much of the Earth. So, at the beginning of the Industrial Revolution, CO2 was 100 ppm more than at the depths of the glaciations. Now it is 120 ppm higher than at the beginning of the Industrial Revolution.

      In fact, the last time CO2 levels are thought to have been this high was more than 2.5 million years ago, an era known as the Pliocene, when the Canadian Arctic boasted forests instead of icy wastes. The land bridge connecting North America and South America had recently formed. The globe’s temperature averaged about 3 degrees C warmer, and sea level lapped coasts 5 meters or more higher.

  • G van Rijswijk

    It is called outgassing. As temperatures increase the CO2 in the oceans transfer to the atmosphere. This process reverses when the oceans cool. Human emissions of CO2 are around 4% of total emissions. Total CO2 in the atmosphere contributes about 3-4% of the greenhouse effect – the major contribution comes form water vapour. It follows that more than 99.5% of the greenhouse effect is natural. Therefore no amount of decarbonisation can reduce the temperature – only natural cycles can do that.

  • Les Johnston

    Another scenario besides the bathtub is to view the earth as a tub of hot water and we are frogs. Fossil fuel combustion (another other greenhouse sources) are heating up the bathwater. Heat loss from the tub is not sufficient to keep up with the heat being applied. The flat earth global warming denying frogs do not realise the bath water is getting too hot to live. There is no way out for any of us, all frogs will one day blissfully perish as the bathwater becomes too hot to survive.