The power of climate feedbacks
The power of feedbacks: Grooves across these rocks in
Central Park bear witness to the time twenty thousand years
ago, when continental ice sheets scoured the bedrock where
New York City now stands.       Photo credit: Simmons Bunting

Critical Point #2: Climate Feedbacks


“Our home planet is dangerously near a tipping point at which human-made greenhouse gases reach a level where major climate changes can proceed mostly under their own momentum.” -James Hansen


As we've seen, the first critical point that everyone needs to understand is the climate has a response lag, which is disguising and delaying most of the effects of the greenhouse gases we've put into the air. By raising the level of CO2 in the air faster than the planet can respond, we've created a package of "on the way" warming headed our way that's three times the actual warming we've experienced so far.

We can still cancel delivery of much of that package of warming, if we quickly bring CO2 in the air back down to a safe level. But since we're still raising the level of CO2 and other greenhouse gases in the air at an accelerating rate, we're letting that opportunity slip away --the package of "future warming" we're sending to our children is getting bigger and bigger every year.



Climate Feedbacks Magnify Temperature Change

There's another reason why it's urgent that we cancel delivery of as much as possible of the "on-the-way" warming by quickly bringing CO2 down to a safe level: climate feedback effects. When that warming does arrive, it will likely unleash an array of vicious cycles that will further destabilize the climate, creating new sources of warming that we won't be able to stop. Studies of Earth's history reveal that our planet is not the stable, self-balancing place we tend to think of it as.

Twenty thousand years ago, the Earth was so cold that a mile-thick ice sheet covered half of North America as far south as present-day New York City, sea levels were 300 feet lower than today, and northern Florida had the climate of present-day Canada. Look back further in time, and there were periods when the planet was so hot that there were no ice sheets anywhere on the Earth, and Greenland had tropical forests with crocodiles. Even further back, at three separate times over the Earth's history, the planet got so cold that the entire globe froze, all the way to the equator, and stayed that way for millions of years.

Why is our planet prone to such wild extremes of temperature? It turns out the Earth's climate system is dominated by feedback effects, natural systems that magnify temperature changes. Whenever small forces nudge the Earth's temperature in a warmer or colder direction, feedbacks magnify those small shifts into massive planetary temperature swings. This is the astonishing discovery of modern climate science: rather than being self-stabilizing, our planet is hyper-reactive, exquisitely sensitive to small temperature influences.

For the last ten thousand years, since the end of the most recent Ice Age, these feedbacks have lain largely dormant -- there haven't been any natural influence strong enough to activate them. It's probably not a coincidence that this period of climate stability was the time that human civilization emerged, and why we tend to think of our planet as a stable, well-mannered place.


Climate feedbacks: The warming from our greenhouse gases threatens to unleash an array
of vicious cycles, creating new sources of warming we won't be able to stop.
Now, the warming from our greenhouse gas emissions is starting to awaken these feedback effects from their ten-thousand year slumber. The danger we face is that once these feedbacks are fully triggered, the system will cross a tipping point, where the feedbacks have a momentum that can't be stopped simply by removing the trigger that got them going.

It's ironic that some people look at the Earth's history of wild temperature swings and conclude that since the climate's changed before, we don't need to worry about how we're changing it now. The real lesson from this history is that because of feedback effects, our planet's climate is on a hair-trigger, responding all out of proportion to influences. Considering that we're now warming the planet ten times faster than the fast warming we know of in Earth's history, complacency is exactly the wrong reaction to our situation.

Here's a run-down of the major feedbacks we are in danger of triggering.


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Arctic Sea Ice: Going, Going....

The Arctic ocean is covered with a layer of floating ice, which expands in winter and shrinks in summer. Because sea ice is white, its sun-reflecting power acts as a central air conditioning system for the north, keeping the Arctic region and the entire planet cool.

Arctic sea ice melt

Up until a few decades ago, the area covered by sea ice in the Arctic at its summertime low point was roughly the area of the continental United States. Starting in the 1970's, and picking up speed ever since, the sea ice has been rapidly melting. As the ice has been shrinking in area, it's also been getting thinner, so ice volume has declined even faster than ice area. From 1979 to 2011, the volume of ice at its September minimum has shrunk by seventy-five percent -- there's only a quarter of what there was a few decades ago.

Current projections are that the Arctic Ocean will have no ice at all during the summer sometime between the late teens and the 2030s. (Sea ice will still form in winter, but the Arctic is in darkness in winter, so winter ice doesn't affect planetary heat balance nearly as much as summer ice.)

Once the summer sea ice is gone, that will give an extra jolt of heating to the entire planet, and particularly to the Arctic region, contributing to other feedbacks in that region.


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Permafrost -- Frozen Carbon, Starting To Thaw

Arctic permafrost map

In the lands surrounding the Arctic Ocean are thousands of square miles of tundra, the open plains of stunted vegetation north of the tree line. Underneath the tundra lies permafrost, permanently frozen soil thousands of feet deep, and that frozen soil is chock full of carbon. As long as the permafrost stays frozen, the carbon remains safely locked up.

The permafrost is starting to thaw. As the frozen soil melts, it decomposes, and releases its carbon into the air. The amount of carbon in the permafrost is greater than the total amount of carbon in the atmosphere. Even a small percentage of this carbon turning into atmospheric carbon dioxide would magnify the planet-heating effect of our own emissions.

What makes this feedback even more powerful, much of the carbon gets released as methane, a super greenhouse gas that has twenty-three times the global warming power of carbon dioxide. As with all feedbacks, once tundra thawing gets started, it becomes a vicious cycle: the more the permafrost melts, the more carbon dioxide and methane get released, warming the climate and melting more permafrost. It's very important that we keep the permafrost frozen.

Permafrost feedback is intimately linked with the sea ice feedback -- the more the Arctic sea ice melts, the more open ocean absorbs sunlight, warming the whole northern region and melting permafrost in the lands surrounding the Arctic ocean.


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Methane Hydrate- The Greenhouse-Gas Belching Sea Monster

Methane hydrate feedback
Methane hydrate: The "ice" that burns.

Deep down on the sea floor of much of the world's oceans are deposits of a strange substance. Called methane hydrate, (sometimes methane clathrate), this compound is a combination of methane and water that forms at the frigid temperatures and bone-crushing pressures of the ocean depths. It looks like ice. If you bring some of it to the surface, the stuff pops and bubbles, as the methane evaporates. If you set a flame to it, the evaporating methane ignites, providing the curious sight of burning "ice".

The key thing about methane hydrate is that it's stable only at low temperature and high pressure. As our planet warms, the extra heat being trapped is steadily working its way into the depths of the oceans. If the temperature of the deep ocean warms sufficiently, the methane hydrates will turn into gas, and bubble to the surface, entering the atmosphere and heating the climate. This isn't just theoretical; it's happened before on our planet.

About 56 million years ago, it appears there was a massive release of methane from deep-ocean hydrate deposits, creating a tremendous spike in global temperatures. Recovery of the climate to temperatures like those before this event took about 100,000 years.

Methane hydrate is a true sea monster from the deep, ready to be awakened. Estimates of the amount of carbon stored in sea floor methane hydrates vary widely, from a little less than the amount of carbon in the atmosphere, to as much as six times the amount in the atmosphere. Either way, because we're talking about the super greenhouse gas methane, release of even a small amount of the methane hydrates would be a fearsome scenario for our civilization.


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Heat and Drought-Stressed Forests Releasing Carbon

Drought forest fire feedback
Amazon forest burning in Brazil in 2005. (Source: Reuters)

Right now, the world's forests absorb a percentage of the carbon dioxide that humanity releases every year. If we continue on our present emissions course, the planet will continue to warm, increasing the frequency and intensity of heat waves, droughts, and wildfires, and stressing the world's forests. Eventually, the forests will cross a tipping point, beyond which absorption of carbon by the forests will go into reverse, and instead of doing us a favor by absorbing carbon, the forests will be come major emitters of carbon into the atmosphere.

In 1998, the world got a foretaste of this. Drought across southeast Asia fueled colossal wildfires that burned much of the forests of Indonesia. Scientists estimate that the amount of carbon dioxide released into the atmosphere by those fires was equal to as much as forty percent all the carbon dioxide produced by humans burning fossil fuels that year.

A heat wave doesn't even need to start a fire to make forests release carbon. Even just a period of very dry, hot weather can stress plants enough to send carbon sequestration skidding into reverse. That's what happened in Europe in 2003. The heat wave that scorched the continent that summer caused European forests and grasslands to send so much carbon into the air that one year that it reversed the effect of four years worth of what those ecosystems normally pull from the atmosphere.

More ominously, the Amazon has just experienced its second "hundred year" drought in a five year period, with a combined carbon release by the two droughts (in 2005 and 2010) probably enough to reverse ten years worth of the carbon sequestration by the world's greatest rain forest.


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Warming Turns Oceans From Friend To Foe

Ocean warming feedback

Right now, the world's oceans are absorbing about 35% of the CO2 we release, much more than any other carbon sink on the planet. That's protecting us from some of the consequences of our emissions.

They are also absorbing most of the heat that the greenhouse gases we've put into the air are trapping, so the oceans are getting warmer. It's basic physics that when water is cold, it can hold more dissolved CO2 than when it's warm -- that's why your beer goes flat as it warms up. As they oceans get warmer and warmer, they'll absorb less and less of our annual carbon emissions. Eventually, the process will go into reverse, and they'll start releasing their stored CO2.

So ocean absorption of CO2 in effect is acting as another lag, as well as having the potential to become a feedback. Also, this absorption of CO2 by the world's oceans is making seawater steadily more acidic, which threatens to unravel marine ecosystems.

This is a very brief overview of some of the main feedbacks. There are many more.


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Lags + Feedbacks = A Climate Emergency

The lag is postponing and disguising most of the warming from the greenhouse gases we're putting into the air, and feedbacks threaten to magnify that warming when it does appear. The failure of the media to educate the public about this has led to two extremely dangerous misconceptions among the public and politicians (that is, among those who don't deny the science altogether).

"Let's wait and see if climate change consequences become severe before we take action." Waiting means we continue to raise the level of greenhouse gases in the air every year, which means increasing the package of "on-the-way" warming we're sending to our kids. By the time the actual warming has grown large enough to be triggering severe effects, the "on-the-way" warming will be truly massive, enough to cause cataclysmic temperature rise, not to mention the climate disruption from the feedbacks it would surely trigger.

"Since our CO2 emissions are warming the planet, we just need to reduce our emissions a little, and that will cool the planet." This is based on a confusion between CO2 emissions and CO2 levels. What's warming the planet is not so much our emissions from this week, or this month, or even this year. What's warming the planet is the accumulation of decades of our emissions, which has raised CO2 levels in the atmosphere.

If we merely cut our emissions, say, by twenty or thirty percent, we'd still be adding to the level of CO2 in the air, and we'd still be headed for catastrophic climate change, only not quite as fast. The CO2 level in the atmosphere is already in the danger zone. We can't afford to continue to let it stay as high as it is now, and we really, really don't want it to rise any further. We need to lower atmospheric CO2, bringing it back down into the safety zone as fast as we can.

Ice-free Arctic Ocean
We need to make sure this projection doesn't become reality. If the Arctic Ocean
goes ice free in summer and stays that way, it will accelerate regional warming,
speeding methane and CO2 release from thawing permafrost and methane
hydrates beneath the ocean floor.

If we don't get CO2 levels down from the danger zone quickly, sooner or later the climate will cross the point of no return. We'll reach a point that between the actual warming, the on-the-way warming, and the climate feedbacks generating new sources of warming, the unraveling climate will have so much momentum that even heroic efforts to end emissions and pull carbon from the air will not be enough to reverse the situation. The climate destabilization will proceed with a momentum of its own, out of our control to stop.

The fact that many of these feedbacks appear already to be starting to activate even at our current level of warming, and we've got three times more warming on the way from the CO2 we've already put into the air, and we're still adding to that CO2 level at a breakneck pace, shows how urgent our situation is.

One group of scientists assessed the situation with these chilling words: "Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects." That was in 2008.

We are facing a climate emergency. It's time for action!


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The Path To A Safe Climate.

To preserve a stable climate for our kids, grandkids, and generations after them, we need to lower the amount of CO2 in the air, rolling back the accumulation of decades' worth of CO2 emissions. And we need to do that fast enough to avoid most of the "on-the-way" warming, fast enough to avoid activating any more feedbacks, and fast enough to deactivate the feedbacks that have already started to awaken.

The first step to reducing the CO2 level is to stop adding to it. That means we stop burning fossil fuels, period. That's an incredibly ambitious task, but it is possible. With a massive global wartime style mobilization, we can switch the world to running 100% on clean energy sources in a very few years (and produce many other benefits in the process).

Second, we take some carbon out of the atmosphere. Bringing our emissions to zero will let natural processes take some carbon out of the air, but we need to bring it down as fast as possible to avoid triggering feedback effects. By re-shaping agriculture and land management around the world, we'll be able to accelerate the speed at which we pull carbon from the air, as well as improving the quality and availability of food.

How much do we need to bring down CO2 levels? For most of the time of human civilization, the level of CO2 in the atmosphere was fairly constant, at around 280 parts per million (ppm). We've raised that to 392 ppm, a forty percent increase. It's estimated that the safe zone is somewhere between 300 and 350 ppm, probably closer to the low end of that range.

CO2 350ppm safe limit
We need to bring CO2 below 350 fast,
before climate feedbacks activate.
                       Image courtesy 350.org

Is it possible for us to do this? Yes! But it means making sure everyone understands we are in an emergency. In an emergency, you find yourself capable of doing a lot of things you normally wouldn't think possible.

The first step is spreading the word, make sure the whole world knows about lags and feedbacks, and why they mean we are in a climate emergency. And we need to spread the word that a rapid transition to a clean energy, carbon-sequestering world is possible, and will bring us many benefits besides saving the climate. And we need to demand that our politicians stand up to big oil and coal, and make their top priority a rapid transition to a clean energy global economy.


Next: What our children and grandchildren may have in store for them if we stay on our present emissions path.