The Global Warming in the Pipeline

This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

A common refrain here on Climate411 is that we need to cut greenhouse gas emissions as soon as possible. One of the reasons we’ve cited numerous times is that, even if we could stabilize greenhouse gas concentrations at today’s levels, some global temperature increase is already locked into the system. This is sometimes called the “warming commitment” or the “warming in the pipeline”.

What’s behind this phenomenon? The short answer is: water, water everywhere.

Earth’s vast oceans buffer the atmosphere from large temperature changes because it takes a lot of energy to change water’s temperature. You know this from everyday life: if you put a pot of cold water on a stove and turn on the burner, you can hold your finger in the water for quite a while before the water starts to warm up.

The same principle applies at the global scale. Oceans cover 71 percent of Earth’s surface. It takes an enormous amount of energy to heat that much water, especially since ocean circulation causes warm surface water to sink and cold deep water to return to the surface. As a result, there is a lag time between when greenhouse gases are emitted to the atmosphere and when temperatures start to rise.

How much warming is in the pipeline? It depends on the level at which greenhouse gases are stabilized. For example, the latest IPCC report calculates that if we held greenhouse gas concentrations steady at 2000 levels, average global temperature would go up another degree Fahrenheit. Concentrations have gone up since then, so the warming commitment for today’s greenhouse gas level is slightly higher than one degree.

The implication of this ocean-induced lag time is that we have less time to act than it first appears. The tipping point for losing the Greenland ice sheet may be just 2.3 degrees Fahrenheit above today. If you factor in the warming in the pipeline, about half of that amount is already gone.

In addition to the oceans’ role, there’s another factor that makes it so important to act today: the long lifetimes of greenhouse gases. How much of an effect does this have? Well, if we cut global emissions deeply enough, the amount of greenhouse gases in the atmosphere would begin to decline. (A couple decades later, temperatures would decline, too.) Unfortunately, it could take centuries for greenhouse gas concentrations to fall all the way back to today’s levels.

The bottom line is that, thanks to the ocean-induced time lag, for the next few decades we’re committed to additional warming. In addition, because greenhouse gases stay in the atmosphere for so long, every ton of global warming pollution we emit today will affect the climate for decades to come, even if we don’t see the effects immediately.

That’s why it’s so important that we start decreasing emissions as soon as possible.

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  1. Posted November 20, 2007 at 10:25 pm | Permalink


    Your article said:
    “For example, the latest IPCC report calculates that if we held greenhouse gas concentrations steady at 2000 levels, average global temperature would go up another degree Fahrenheit.”

    How long would take to go up that one degree F?

  2. Posted November 20, 2007 at 10:38 pm | Permalink

    Let’s hope there’s some as yet unknown atmospheric reaction that could slow down the warming, such as an increase in low-level clouds when temperatures reach a certain level. From what I read, forecasting clouds in climate models is very difficult. Who knows? (I know…wishful thinking)

  3. Posted November 21, 2007 at 12:05 pm | Permalink

    Hi kenzrw,

    If we could hold concentrations steady at current levels, the additional warming would take several decades. You can see this in the second figure of my post “Climate Models: How They Work”.

    As for some yet unknown atmospheric phenomenon to slow down warming… we know that sulfate aerosols reflect sunlight and have a cooling effect. As a result, both volcanoes and geoengineering could conceivably “buy time”. But we can’t control volcanoes and, as Bill explained in his post, there are lots of risks about geoengineering!

  4. Posted November 21, 2007 at 7:48 pm | Permalink

    Geoengineering scares me, more for what we don’t know than anything else (i.e., how would it effect the ecosystem other than the cooling). Isn’t there already a company in the Pacific that’s supposed to ‘seed’ the ocean with iron so the ocean can make more algae, thus becoming a carbon sink? I hope there’s not too many others going off willy nilly like this without proper controls. Anyway, doing something like artificial carbon sequestering makes the public lazy and not want to cut back on emissions.

  5. Posted November 24, 2007 at 1:42 pm | Permalink

    This may be God’s greatest challenge to humanity. Solving this problem would require civilizations to change and to actually care about their fellow man. Many nations consumed by fear will prevent the necessary changes regarding energy production to prevail. It seems to me that science is concrete on the subject of global warming, and the lawyers and political leaders are ignorant. As are most people who have not been effected by anything more than $3/ gallon.

    Humans need to change the way they are living. I am feeling very skeptical that we are capable of such simple but great change.

  6. saluki
    Posted November 25, 2007 at 10:31 pm | Permalink

    I see that there is a lot of political activism on this blog, but the discussions about the science of global warming seem to be very limited. This worries me. I would like to ask a few questions regarding the science.

    1. It seems to be treated as axiomatic by the man made global warming advocates that as CO2 in the atmosphere increases, global temperature increases. But when we look at the historical record of global temperature versus global CO2, temperature rises seem to be leading C02 rises in most cases and by as much as one hundred years. It appears that increasing temperatures cause increases in CO2 rather than the other way around.

    2. The earth constantly undergoes changes in climate. We have had much higher temperatures – 10 to 15C higher than today. We have had CO2 level almost 10 times as high as today. We have had completely melted ice caps. We have had rates of change of temperature increase that are 4 times what we are experiencing today. All of this happened long before the first redneck stepped into the first SUV. So why do we need mankind to explain the current rises in temperature?

    3. When we use historical thermometer records to tell us about temperature change in the recent past, why don’t we account for the “islands of heat” problem that is produced by taking temperature readings in areas where the population has significantly increased over the recent past.

    4. Why were temperatures higher than today in the middle ages, and why did it produce prosperity instead of doom?

    5. Why is it that most of the temperature rise that happened in the last hundred years or so happend in the early part of the century when industrializations and automotive traffic were almost insignificant?

    6. With the earth having experienced much more radical temperature extremes and having recovered quite nicely, over the last 65 million years, why are people trying to convince us that suddenly, if mankind doesn’t act immediately, the world will go to hell in a handbasket?

    7. Why do the ocean levels in the Maldives seem to be going down rather than up?

    8. What do you think is untrue about what this professor of climate has to say?

  7. GWG1
    Posted November 28, 2007 at 3:11 pm | Permalink

    Please watch and spread the word about global warming!

  8. Jay Alt
    Posted December 4, 2007 at 2:28 pm | Permalink

    kenzrw writes:
    Isn’t there already a company in the Pacific that’s supposed to ‘seed’ the ocean with iron so the ocean can make more algae, thus becoming a carbon sink?

    That idea seems to have hit a problem recently.

    ‘Fix’ For Global Warming Discredited By New Research

  9. Posted December 12, 2007 at 3:41 pm | Permalink

    There is extensive discussion of science on this blog. See the list of categories? There are 63 in Science. Click the link and take a look. All your questions will be answered.

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