Varun Sivaram

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Hurricane Sandy: Is There Anything We Can Do About Climate Change Soon?

by Michael Levi
October 31, 2012


The East Coast is slowly returning to normal life after Hurricane Sandy – and pundits, scientists, and journalists are quickly diving into a debate over what the storm says about climate change. I have nothing useful to add on that matter. But I do wanted to shed light on an important related question that has come up: is it even possible to change the course of climate change over the next fifty or so years?

The uninformed conventional wisdom is something like “of course we can change things if we start shifting to clean energy”. As I explain below, that’s not really true. David Roberts does a nice job of laying out what I’d call the “informed conventional wisdom” in a series of tweets (!) that I’ve concatenated here:

“Realtalk: The oceans will continue to rise for at least 50 years no matter what we do. We can only affect the latter half of century. There’s nothing Obama (or Bush, Clinton, Bush, or Reagan) could have done to prevent Sandy. Climate don’t work that way. Big time lags. The mega-hurricanes that we CAN prevent are the ones that will bedevil our children in the latter third of this century. The best we can do for ourselves and those alive in the next 50 years is enhance the resilience of our communities & infrastructure.”

My instinct tends in the same direction: the climate system has an immense amount of inertia. But, after some thought, I’m inclined to conclude that reality is a bit more messy. We actually do have some meaningful potential influence – albeit limited – over what happens in the coming decades. To understand this it’s useful to focus on three distinctions.

Carbon dioxide versus everything else

Changes in carbon dioxide emissions take a long time to have any impact on the climate system. That’s because of inertia in the both oceans and the atmosphere. But changes in emissions of shorter lived gases can affect the climate system more rapidly. That’s because, even though their impact is still constrained by intertia in the oceans, they aren’t as constrained by inertia in the atmosphere.

A recent paper in Science by Shindell et al helps shed light on this distinction. It examines a suite of measures aimed at reducing carbon dioxide emissions along with another suite aimed at cutting emissions of methane and black carbon (referred to as short lived forcers). A plot of projected temperatures taken from the paper is shown below.

Two things immediately become clear. First, consistent with the “informed conventional wisdom”, measures that reduce carbon dioxide emissions have essentially no temperature impact for thirty years. (The actually make things a tiny bit worse, presumably because shutting down coal plants reduces emissions of planet-cooling sulfur dioxide.) Second, though, cutting emissions of methane and black carbon reduces transient temperatures starting right away. By 2050, they cut global average temperatures by about half a degree Celsius relative to trend. Eyeballing the chart in Shindell et al suggests that much of that benefit is realized by 2030. One can reasonably debate whether the modeled emissions cuts are realistic, but as far as the climate system goes, these outcomes are plausible.

Temperature versus sea level

Storm damage is potentially influenced by at least two factors related to climate change: temperature (which can provide storms with energy) and sea level (which can make low lying areas more vulnerable to start with). Everything I’ve just written refers to temperatures. Sea levels, unfortunately, are slower to respond.

To put some numbers to this, I cooked up a highly unrealistic but still informative scenario. I started with a well known emissions scenario in which global carbon dioxide concentrations ultimately stabilize around 450 ppm (i.e. the sort of scenario that policymakers often talk about). Then I tweak that scenario so that methane emissions plummet in 2015 and stay low through 2100. The projected temperature outcomes (using MAGICC) look like the following:

The temperature rise by 2100  in the case with near-term methane emissions cuts is about 0.3 degrees less than in the case without those cuts. Even more striking, though, is that 100 percent of that temperature reduction is realized by 2050, and that 55 percent of it is realized by 2030.

The picture looks  quite different, though, for sea level rise:

The sea level rise by 2100 in the case with near-term methane cuts is about 4 centimeters less than in the case without those cuts. Only half of that, though, is realized in 2050, and mere 20 percent of it shows up by 2030.

The details of these projections, of course, are sensitive to the choice of model and the emissions path. But the basic point – you can do considerably more about temperatures than sea levels in the short run – is solid.

Short term versus long term

It is important to keep in mind that the near-term benefits that accrue from cutting short-lived forcers comes at a long-term cost. Shindell et al don’t show projections for the case where their methane and black carbon reducing measures are implemented with a delay. [ML: Important correction appended: They explore this possibility in the online supplementary material. See the comments section for Drew Shindell’s enlightening explanation, which largely tracks with how I see things. My mistake in the original.] If they did, they would find that delaying the cuts, but still implementing them eventually, would help keep down the rate of temperature increase precisely when temperatures are at or near their highest – and thus presumably when climate-sensitive systems are most stressed. Scientists often emphasize that rapid warming can be particularly damaging. The upshot is that near-term measures to cut emissions of things like methane and black carbon, while valuable in suppressing near-term warning, may have a long-term price in climate impacts. I personally think that many near-term steps have benefits – not only for climate but also for local air pollution and human health – that outweigh these downsides. But that doesn’t mean that the downsides don’t exist and shouldn’t be considered.

Post a Comment 6 Comments

  • Posted by Drew Shindell

    In our paper (Shindell et al., Science, 2012), we do in fact show projections for the case when methane and black carbon control measures are implemented with a delay (Figure 3 in the Supplemental Online Material). As expected, late implementation has an effect that comes into play later in time but has a similar impact on temperature in the long term. While I agree that many human and natural systems are likely to be strongly affected by the maximum rate of change, it’s not obvious when that will be. It could be near the time of peak temperatures in the distant future, but if society moves gradually towards reduced CO2 it could instead be quite soon. It really depends upon the emissions trajectory that the world takes, so it’s not possible to say if measures targeting near-term or long-term climate change are more likely to reduce the maximum warming rates. That said, I fully agree that downsides should be considered, and I too feel that the benefits of the near-term measures outweigh their downsides.

  • Posted by David B. Benson

    Of course 450 ppm means that eventually most of the Greenland and Antarctic ice sheets melt. What has to happen is to actually remove excess CO2. One way is to grow an enormous number of trees:

    Irrigated afforestation of the Sahara and Australian Outback to end global warming
    (where the full paper is open access).

  • Posted by Michael Wara

    Great post. Good to highlight these issues.

    The Shindell et al. article previews some of the issues that will be highlighted in the fifth assessment from IPCC WG1. One take home from all of this is that, contrary to popular understanding of climate change, the science is NOT saying the same thing that it was in 1897 (Arrhenius) or 1990 (Watson). The “we knew all this a long time ago” statement is still true for CO2. But for everything else, there have been tremendous strides that point to new opportunities to reduce the probabilities of crossing dangerous thresholds.

    My own take away is that we really need to think hard about whether the current Climate regime’s single-minded focus on 100y GWP has outlived its usefulness. (Full disclosure, I’m working on a paper that presents options for moving beyond it from within the regime).

  • Posted by Philip Haddad

    The real cause of global warming is the heat released by our consumption of fossil fuel and nuclear power. The CO2 has very little to do with it. Kyoto totally ignored the heat release,. Although , CO2 does absorb infra red radiation the amount of heat is miniscule compared to the amount of cooling provided through photosynthesis in removing 5000 btus of energy for each pound of CO2 converted to trees. The sooner we target heat, instead of CO2, the better. The EPA has designated CO2 as hazardous to human health, (THE CARBONIC PLAGUE) has passed laws taxing CO2 emissions, and upheld by the Supreme Court, mind you. It is inappropriate to tax companies for their CO2 emissions and reward companies that remove the CO2. The heat has been released in either case! Some proponents of the CO2 myth try to make us believe that the level of CO2 is now so high that solar heat alone will cause the temperature to continue rising even if we used no more energy. This is preposterous.

  • Posted by SidAbma

    I guess my only 2 bits worth in this is America has to increase it’s natural gas energy efficiency.
    Natural gas is becoming America’s source of Energy Security and Energy Efficiency. America apparently has lots of it.
    It heats our buildings, and fuels our industries. It provides 1/2 of our electricity and is growing as the coal plants are being converted to natural gas. Soon highway trucks, city buses and garbage trucks, taxi’s and commuter cars will be powered with natural gas. Railroad trains and ocean going ships are talking about this fuel.
    This is great, as it will help reduce emissions- as long ass it stays a reasonably cheap fuel.
    Natural gas is an energy source that can be consumed to near 100% energy efficiency. Hard to do coming out of a tail pipe.
    But stationary natural gas appliances also have chimney’s, and it is these locations that our government and industries and utilities have to work at making more efficient.
    Why waste all this HOT energy up all these chimney’s across the country? The technology of Condensing Flue Gas Heat Recovery can have all these locations recovering this energy out of the exhaust gases, so that this recovered energy can still be used back inside the building or facility, instead of being blown into the atmosphere as HOT exhaust.
    Global Warming? Climate Change?
    It’s a decision. Do we as proud Americans want to make a difference?
    We have one chance to use this natural gas energy.
    What is not wasted today will be there to be used another day.
    Increased natural gas energy efficiency = Profit
    Increased natural gas energy efficiency = Reduced Emissions
    Can we make America the place we want it to be?
    Profitable and a clean environment.

  • Posted by David B. Benson

    I don’t think Philip Haddad will be back to check, but he has the physics completely wrong. He would do well to read “The Discovery of Global Warming” by Spencer Weart:
    for starters.

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