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The Student News Site of Macalester College

The Mac Weekly

The Student News Site of Macalester College

The Mac Weekly

Prof Talk: Louisa Bradtmiller, ES, on Copenhagen, the past 500,000 years, the next 100, the ocean and trouble

By Hazel Schaeffer

The Mac Weekly: Why is an understanding of oceans import to our understanding of climate change?Prof. Bradtmiller: I study the impact of the climate change on the oceans, but more specifically I study the impact of oceans on climate change. The oceans are important for understanding climate for two reasons. One is that they are a major mechanism for heat transport in the climate system. Most of the sun’s radiation comes into the earth around the equator in the tropics, and part of how it gets to the mid-latitudes, where we are, or to the poles, is through ocean circulation, either surface currents or larger scale circulations.

The reason more relevant to what I study is that the ocean is a big reservoir for carbon that exchanges easily with the atmosphere. Carbon dioxide in the atmosphere is what most people think of when they think about global warming. In fact, carbon dioxide is constantly moving between the atmosphere and plants (both on land and in the water) and being dissolved in water, so the ocean holds a lot of carbon. Actually, most of the carbon dioxide that humans have emitted so far has ended up in the ocean.

What I study specifically is how the climate changed before people started emitting carbon dioxide . I look at ocean sediment records and [try] to pinpoint the mechanisms that helped transfer carbon from the atmosphere to the oceans during glacial periods, and the opposite: how the carbon gets back into the ocean during inter glacial periods-warm periods, like we are in right now).

TMW: Have human actions disrupted the natural transfer of carbon?

Prof. Bradtmiller: Yes. What humans are doing is taking carbon out of the rock reservoir. We’re drilling for oil and coal and putting that carbon back into the atmosphere much faster than it would have gotten there naturally through erosion. We don’t affect the carbon transfer from the ocean to the atmosphere. But, like I said, we are putting a lot of carbon into the ocean, which is acidifying it.

A lot of organisms in the ocean make calcium carbonate shells, which dissolve in acid. The more acidic we make the ocean, the harder we make it for those organisms to form shells. They build those she shells for a reason. If you disrupt their ability to form shells, all of a sudden you’ve disrupted a whole ecosystem . The [organisms] are important because there are a lot of them. There are orders of magnitude more photosynthesis that happens in the ocean than on land. The [organisms] have a huge impact on the carbon system because they are undergoing photosynthesis and because they incorporate carbon into their shells and [their soft tissue].

Plants on land take up carbon dioxide and give up oxygen through photosynthesis. If you’re making it harder for plants in the ocean to form calcareous shells, you’re diminishing the amount of oxygen they can take up. There are also effects on the pH of the ocean. The more carbon is dissolved in the ocean, the more acidic it becomes, which makes it harder for them to absorb carbon.

The capacity of the ocean to hold carbon is only so large. The more carbon we put in the atmosphere, the less able the ocean is to continue to take up carbon. The proportion of carbon that stays in the atmosphere is probably going to increase in the future, which is trouble on top of trouble already.

TMW: How much can the chemical balance of the ocean change before it becomes dangerous for the organisms living there?

Prof. Bradtmiller: The ocean is a buffered system. You can keep adding acid and it only changes the pH a little bit, but at some point you cross a threshold when you add enough acid that the pH changes dramatically. We haven’t hit that point yet, but we certainly could.

TMW: Changing the topic, in your opinion, why did the talks at Copenhagen fail?

Prof. Bradtmiller: People have a very hard time thinking about problems in the future, and that’s something the Econ. department or the Psychology department knows way more about than I do. It seems like there is no pressing reason to act. One reason is that every time you have a cold week in January, everybody throws up their hands and says, “It’s freezing, there’s no global warming.” The other reason is purely economic. The United States is a big emitter of green house gases, but China has overtaken us as the number one. They are a developing economy, and perhaps fairly ask the question, “The major Western economies were allowed to develop however they saw fit- why should we be restricted from doing the same thing?”

One of the goals of Copenhagen was to come up with a pool of money for developing countries to help offset the costs of implementing more carbon neutral technology. They arrived at a number of about how much money it should be, but no one has put actual money into it yet.

The U.S. could probably have taken a little bit more leadership, but the U.S. took a lot more leadership than it has in the past eight years, which was a positive step. And most of the countries that attended agreed in principal to the accord that was made and said that they intend to submit plans to reduce emissions. In our case, I think 17 percent by 2020. The deadline for [submitting plans] is January 31st. If a lot of countries come up with that by the 31st, Copenhagen will be a lot less of a failure than it seems now. The big failure was not agreeing on binding emissions targets. Without that, they are just kind of relying on everyone’s good will.

TMW: What do you think of the U.S.’s target of decreasing emissions by 17 percent?

Prof. Bradtmiller: Well, it’s more than we are doing now. It represents actually trying to do something, and that will raise the issue in people’s conscience. It’s not fast enough to prevent actual bad things from happening. The most recent International Panel on Climate Change has pretty frightening projections for temperature in the year 2100 … This is their best guess, but the people who know most about it say that it will be a lot warmer, and in places where it is really unfortunate, like the poles. You’re talking about melting a lot of ice and raising sea levels. A huge percentage of the world’s population lives near the coasts. The other places that will be disproportionally affected are places that aren’t doing very well, like sub-Saharan Africa. Nothing has happened so far that seems to divert us from that path [suggested by the IPCC]. In the U.S. we aren’t going to be that bad off. That’s the problem: the disconnect between the people causing the problem and the people that are suffering the consequences of it.

TMW: Do you think Americans will not be motivated to act, short of some visible “natural” disaster?

Prof. Bradtmiller: Yes. I think that negative consequences are the most likely thing to get people to act. Because of the way the climate system works, it takes a long time for it to respond. By the time you start seeing negative effects and get motivated to do something, the worry is that it will be late to stop even worse things from happening.

TMW: Does Macalester have a responsibility as an institution to combat climate change?

Prof. Bradtmiller: Macalester’s sustainability plan includes the goal to become carbon neutral by 2025. I think having a goal like that, regardless of what the government is doing, is exactly the right attitude, taking responsibility for what we can control.

TMW: Why is Paleoceanography and Paleoclimate important for an understanding of climate change?

Prof. Bradtmiller: Paleoclimate gives us a frame of reference for modern climate change. The news just came out [Monday] that 2009 was the second warmest year since 1880 and that the decade 2000-09 was the warmest decade on record. But our record is only 200 years long. We need something to compare that 200 years to because maybe that 200 years was just a really cold time period. But the paleoclimate record tells us that we are getting warmer than most analogous times in earth history, and it also te
lls us something about what might happen if carbon dioxide concentration continues to increase.

It’s not that this is an unprecedented rate of carbon dioxide increase in the atmosphere, but the periods we know about when the carbon increased this fast, there were lots of extinctions and lots of major reorganizations of ecosystems. We have analogs for changes this fast, and they don’t look very good for living things.

TMW: Does the fact that the earth does naturally go through warming and cooling systems lead some to believe that we are not responsible for global warming?

Prof. Bradtmiller: Yes . If you look at the last 500,000 years, climate does a pretty particular thing. It stays stable for about 10,000 years at about the temperature we are at right now.
We have a pretty good idea what climate does when it’s left to its own devices. If you plot temperature over the past 200 years on top of what we think a natural cycle looks like, you can see that those two things are different. So yes, climate definitely varies on its own, and we are outside that variability. There’s no external force that you can point to, besides humans, that should have caused it to change from that natural 100,000 year cycle.

Send suggestions for future Prof Talks to [email protected]

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