Concentration of CO2 in the Atmosphere

Wallace Broeker’s Final Warning

Wallace Smith Broecker. Image: Wikipedia

George Harvey

Wallace Smith Broecker, the man some people have called the “grandfather of modern climate science,” died on February 18, 2019. He was 87 years old and had been suffering from heart disease for decades. He worked despite his illness, and he addressed other climate scientists in an important discussion only a week before he died. Speaking to them, he gave the people of our planet a warning.

Because of his health, he was not able to meet his colleagues face to face. Instead, he had to give a recorded message. He sat in a wheel chair and breathed air enriched with oxygen from a tube. He knew he was in rough physical condition, but he told his audience, “My mind is running pretty smoothly.”

His message was simple. We are not moving fast enough to stop climate change, and we have to work much, much harder. To do otherwise is unacceptable for the sake of the survival of humanity. He also spoke of one way we might stop it, although he only considered it as a last ditch effort. It would be a possible option even if we wait too long for emissions reductions and conventional carbon draw-down methods to work. That way is called “geo-engineering.” It is not the most desirable approach but may be what we will have to do, if we wait too long.

Broecker had worked a long time in the field of climate science and in disciplines to which it is related. In 1975, he published a paper called, “Climate Change: Are We on the Brink of a Pronounced Global Warming?” The title was the first mention of global warming that made any impact on the minds of many people.

Broecker also brought popular attention to the recently discovered “ocean conveyor belt,” a system of circulating currents that includes the Gulf Stream. He worked on the issues of how the ocean currents and temperatures are related to climate change. His work covered the current situation, but he also looked at the whole question from a historic perspective, using scientific evidence and dating techniques.

In his final talk, Broecker urged scientists to be ready for geo-engineering. Again, that is not to say that he was urging actual geo-engineering. He regarded it as a last resort, but one we should study so we can be ready if we need it.

The issue of geo-engineering is best illustrated by an event in 1991. Mount Pinatubo, a volcano on the Philippine island of Luzon, suddenly started to erupt. While the quick buildup of the eruptions was interesting in itself, and the emergency evacuation of thousands of people was widely talked about, climate scientists are interested in another aspect of the event.

Along with about 10 billion tons of magma, the eruption of Pinatubo put 20 million tons of sulfur dioxide (SO₂) into the atmosphere. In terms of the material it ejected, it was the largest eruption since Krakatoa’s, in 1883. The effect of this was a global cooling of 0.5° C (0.9° F) that lasted for well over a year.

It happens to be the case that SO₂ and related sulfur compounds are precursors for sulfuric acid (H₂SO₄). H₂SO₄ reflects quite a lot of sunlight back into space, dimming the surface of the Earth, allowing it to cool off. So the thinking is that all we need to do to reverse the global warming that has happened so far is to dump about 20 million tons of SO₂ into the atmosphere every year or two. Of course, as we emit more carbon dioxide (CO₂), we would have to increase the amount of SO₂.

I know there are probably many readers who want to shout at this point, “That’s crazy!” I do not blame them one bit. It is crazy! And that is why Broecker wanted us to study it as a potential last resort. He hoped we would never have to use it, but if we need to use it, we should use it as intelligently and carefully as we can.

Coal-fired power plants have been emitting SO₂ for over a century, and this has been returning to Earth as acid rain containing H₂SO₄ along with some sulfurous acid (H₂SO₃). It melts marble, kills fish, kills birds, inhibits growth of vegetables, destroys paint on cars and buildings, and eats iron, not to mention what it does to our health. That is why the Environmental Protection Agency requires that power plants take care not to emit it above certain low levels.

Putting SO₂ in to the atmosphere is actually a type of chemotherapy, intended to keep the Earth alive. No one would choose chemotherapy, unless there is no other option. No sane person would choose to push 20 million tons of SO₂ into the air we breathe without a really good reason. The problem is that if we do not act faster to reduce CO₂ emissions, SO₂ emissions may come to be our only hope.

Please notice that our best hope is stated in the conditional clause: Act faster to reduce CO₂ emissions. If we can do that, we are doing our best to avoid the worst.

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