Modelling Geoengineering

Later in my career as a climate modeller, I expect to spend a lot of time studying geoengineering. Given the near-total absence of policy responses to prevent climate change, I think it’s very likely that governments will soon start thinking seriously about ways to artificially cool the planet. Who will they come to for advice? The climate modellers.

Some scientists are pre-emptively recognizing this need for knowledge, and beginning to run simulations of geoengineering. In fact, there’s an entire model intercomparison project dedicated to this area of study. There’s only a small handful of publications so far, but the results are incredibly interesting. Here I summarize two recent papers that model solar radiation management: the practice of offsetting global warming by partially blocking sunlight, whether by seeding clouds, adding sulfate aerosols to the stratosphere, or placing giant mirrors in space. As an added bonus, both of these papers are open access.

A group of scientists from Europe ran the same experiment on four of the world’s most complex climate models. The simulation involved instantaneously quadrupling CO2 from preindustrial levels, but offsetting it with a reduction in the solar constant, such that the net forcing was close to zero.

The global mean temperature remained at preindustrial levels. “Great,” you might think, “we’re home free!” However, climate is far more than just one globally averaged metric. Even though the average temperature stayed the same, there were still regional changes, with cooling in the tropics and warming at both poles (particularly in their respective winters):

There were regional changes in precipitation, too, but they didn’t all cancel out like with temperature. Global mean precipitation decreased, due to cloud feedbacks which are influenced by sunlight but not greenhouse gases. There were significant changes in the monsoons of south Asia, but the models disagreed as to exactly what those changes would be.

This intercomparison showed that even with geoengineering, we’re still going to get a different climate. We won’t have to worry about some of the big-ticket items like sea level rise, but droughts and forest dieback will remain a major threat. Countries will still struggle to feed their people, and species will still face extinction.

On the other side of the Atlantic, Damon Matthews and Ken Caldeira took a different approach. (By the way, what is it about Damon Matthews? All the awesome papers out of Canada seem to have his name on them.) Using the UVic ESCM, they performed a more realistic experiment in which emissions varied with time. They offset emissions from the A2 scenario with a gradually decreasing solar constant. They found that the climate responds quickly to geoengineering, and their temperature and precipitation results were very similar to the European paper.

They also examined some interesting feedbacks in the carbon cycle. Carbon sinks (ecosystems which absorb CO2, like oceans and forests) respond to climate change in two different ways. First, they respond directly to increases in atmospheric CO2 – i.e., the fertilization effect. These feedbacks (lumped together in a term we call beta) are negative, because they tend to increase carbon uptake. Second, they respond to the CO2-induced warming, with processes like forest dieback and increased respiration. These feedbacks (a term called gamma) are positive, because they decrease uptake. Currently we have both beta and gamma, and they’re partially cancelling each other out. However, with geoengineering, the heat-induced gamma goes away, and beta is entirely unmasked. As a result, carbon sinks became more effective in this experiment, and sucked extra CO2 out of the atmosphere.

The really interesting part of the Matthews and Caldeira paper was when they stopped the geoengineering. This scenario is rather plausible – wars, recessions, or public disapproval could force the world to abandon the project. So, in the experiment, they brought the solar constant back to current levels overnight.

The results were pretty ugly. Global climate rapidly shifted back to the conditions it would have experienced without geoengineering. In other words, all the warming that we cancelled out came back at once. Global average temperature changed at a rate of up to 4°C per decade, or 20 times faster than at present. Given that biological, physical, and social systems worldwide are struggling to keep up with today’s warming, this rate of change would be devastating. To make things worse, gamma came back in full force, and carbon sinks spit out the extra CO2 they had soaked up. Atmospheric concentrations went up further, leading to more warming.

Essentially, if governments want to do geoengineering properly, they have to make a pact to do so forever, no matter what the side effects are or what else happens in the world. Given how much legislation is overturned every time a country has a change in government, such a promise would be almost impossible to uphold. Matthews and Caldeira consider this reality, and come to a sobering conclusion:

In the case of inconsistent or erratic deployment (either because of shifting public opinions or unilateral action by individual nations), there would be the potential for large and rapid temperature oscillations between cold and warm climate states.

Yikes. If that doesn’t scare you, what does?


Recommended Reading

A lot of great articles reflecting on the Durban talks have come out in the past few weeks, particularly in the mainstream media. Some of my favourites are Globe and Mail articles by Thomas Homer-Dixon and Jeffrey Simpson, The Economist writing that climate change, in the long run, will be more important than the economy, and George Monbiot on how much money we spend bailing out banks while complaining that cutting carbon emissions is too expensive.

Share your thoughts, and other articles you like, in the comments.

Climate Change and Young People

Cross-posted from NextGen Journal

What is the most important policy issue facing today’s young people? Climate change might not seem like an obvious contender, as it feels so distant. Indeed, the majority of impacts from global warming have yet to come. But the magnitude and extent of those impacts are being determined right now. Only today’s young people will still be around to witness the effects of today’s actions.

Many people see climate change as just another environmental issue that will only impact the polar bears and coral reefs. In fact, it’s far more wide-reaching than that. An increase of only a few degrees in average global temperature will affect human systems of all kinds: agriculture, public health, economics, and infrastructure, just to name a few.

Dr. Gavin Schmidt, a climate modeller at NASA’s Goddard Institute for Space Studies and one of the world’s top scientists studying global warming, says that significant changes in global temperature can be expected within the lifetimes of young people alive today – “somewhere between two, three, five degrees Celsius, depending a little bit on the scenario, and a little bit on how sensitive the climate actually is.” It might sound like a small change, until you look back at the history of the Earth’s climate and realize that the last ice age was only around 5 degrees Celsius cooler than today. Additionally, the rate of warming (which is the more important metric for the ability of species, including people, to adapt) is higher today than it has been at any time for at the least the past 55 million years. Human technology has far surpassed the natural forces in the climate system, to the point where significant future warming is inevitable. In fact, says Schmidt, the climate system “hasn’t even caught up with what we’ve put into the atmosphere so far. As it continues to catch up, even if we don’t do anything else to the atmosphere from now on, we’ll still see further warming and further changes to the climate.”

However, the future is still quite malleable. Two degrees of warming is bad, but five degrees is far worse, and the difference between the two ends of the spectrum will depend on what we decide to do about the problem. Since our emissions of greenhouse gases, especially carbon dioxide, are causing global warming, the solution is self-evident: cut our emissions, as quickly as we can reasonably do so. Implementing this solution is not so simple, as fossil fuels are currently highly integrated into the global economy. Luckily, free-market mechanisms exist which alter the price signals of fossil fuels to better reflect the damage they cause. A revenue-neutral carbon tax, which is offset by reductions in income taxes or paid back evenly to the public as a dividend, is one solution; a cap-and-trade program, which treats carbon emissions like a currency, is another. While virtually nothing has been done in North America to cut emissions, the rest of the developed world has made a pretty good start.

Here in North America, the outlook for action is somewhat bleak. In the United States, says Schmidt, many people “perceive the science itself – just describing what’s going on and why – as a threat to their interests…they choose to attack the science and they choose to attack the scientists.” The Republican Party has adopted this strategy of denial, to the point where top presidential candidates such as Michelle Bachmann and Rick Perry truly believe that climate change is a hoax scientists cooked up to get grant money. The Democrats largely accept the science, but after nearly a full term in office, President Barack Obama hasn’t made any progress on the cap-and-trade program he promised upon his election. In Canada, Prime Minister Stephen Harper has repeatedly said that he will follow whatever actions the United States takes, or does not take, on climate change policy.

It seems that action necessary to mitigate global warming won’t be taken unless citizens demand it. Otherwise, emissions will likely continue unabated until the problem is too severe to ignore any longer – and even then, the situation will get worse for decades while the climate system catches up. “No action,” says Schmidt, “is a decision in and of itself.”

What decision, then, will we make? Will we get our act together in time to keep the warming at a tolerable level? Or will we choose to let it spiral out of control? Will future societies look back on us with resentment, or with admiration? Remember, you and I are part of those future societies. But we are also part of today’s.

Thousands of years from now, it won’t matter what the US deficit was in 2011, or which nations went to war with each other, or how much we invested in higher education. These issues matter a great deal to people today, but they are very transient, like many aspects of human systems. Climate change, though, will alter the earth on a geological timescale. It will take the planet around one hundred thousand years to undo what we are doing. We are leaving behind a very unfortunate legacy to the entirety of future human civilization, and all life on Earth – a legacy that is being shaped as you read this; a legacy that we could largely avoid if we chose to.