Liz’s Leadership Salon Series—Young Talent: America’s Promise
remarks by robert kopp
Science, Technology, and Envrionmental Policy Postdoctoral Fellow
Woodrow Wilson School of Public & International Affairs / Department of Geosciences
Princeton University, Princeton, NJ 08544 USA
February 28, 2008
echoes of ancient times:
climate change in earth’s past and our future
Over the past few years, you’ve probably heard a good deal about global warming and climate change. I hope today to provide you with a bit of a different perspective on how human actions fit into the context of ancient climate change, and what that suggests for our future.
I’m a geologist: I study rocks and sediments and try to unravel our planet’s post from them. I’m a geologist for two main reasons. One is that I like stories, and that I like history. I spend my time reading stories written in rocks — written in their textures, their arrangements, their physical properties, their chemistry, their composition. Rocks chronicle the fantastic epochs of our planet’s past: times when crocodiles bathed in the Arctic sun; times when all the land and most of the ocean were frozen beneath a mantle of ice; battles between cyanobacteria that made oxygen and the oxygen-free biosphere into which they were born.
But I’m a geologist for another reason, too. Conditions on Earth’s surface are a product of planetary cycles. Elements course through the solid Earth, the ocean, the atmosphere, and living organisms. Energy from the Sun is captured by plants and is passed from them to the rest of the living and non-living Earth. These intertwined flows determine whether our planet is hot or cold, wet or dry, hospitable or inhospitable.
In the span of a couple centuries, humankind has gone through an adolescent growth spurt. We have taken a place alongside the cyanobacteria as one of the Great Powers of the world. We have the power to destroy ourselves and many other species along with us. But by learning from the past we can acquire the wisdom to be good stewards and wield our new power responsibly.
As you probably know, Earth’s temperature is fundamentally controlled by three basic properties: how much light from the Sun strikes the Earth; how much of it gets reflected back; and how much radiation, having reached the Earth’s surface, is kept there by the Earth’s atmospheric blanket of heat-trapping gases. The amount of light and heat from the Sun has been slowly increasing over Earth’s history, but over the timescales we’re concerned about, it’s basically constant. In contrast, the planet’s reflectivity and the amount of heat-trapping gases like carbon dioxide can change a great deal.
If the planet were black and had no atmosphere, it would have an average temperature of about 40° F. Oceans, forests, and asphalt are almost black — they have low reflectivity and absorb a large majority of incoming light. Ice, snow and clouds, in contrast, are highly reflective. So ice helps keep the planet cool, and melting ice and replacing it with dark water or land warms the planet. Overall, our planet reflects about 30% of incoming light; so without an atmosphere, it would be a rather frigid 0° F.
It’s not, of course; on average, our planet is 59° F, due to the effect of heat-trapping gases like carbon dioxide and methane. It’s very important to life on our planet that these gases are there. But changes in these gases can therefore have dramatic effects on our planet’s surface. Doubling carbon dioxide levels, for instance, will most likely warm the planet overall by about 5° F, though the upper range models are higher. 250 years ago, for reference, carbon dioxide levels were around 280 ppm; right now, they’re at 380 ppm, and many scientists believe we should try to keep them below 450 ppm, or certainly not more than 550 ppm, one doubling above pre-industrial levels. Without action, we’re probably on track for about 900 ppm by the end of the century and a warming of 7–11° F.
Even 11° F may not sound like too much — the sort of variability we experience in the Northeast from day to day. But it is a real difference. In the northeastern US, average winter temperatures have gone up by almost 5° F since 1970. And if you’ve lived in the region for much of that time, I’m sure you’ve noticed. It’s not your imagination — and that’s just the local expression of a global 1° F temperature rise.
But to understand what a global 5° F warming means, you have to go back in time. So I’m going to take you on a little journey into Earth history. We’re going to have to travel into periods so ancient there’s no way of truly understanding time except by analogy. Humans just aren’t equipped to understand what a hundred thousand years, let alone a billion years, means.
Imagine the Earth as a human being — we’ll call her Dr. Earth. One year in her life as a hundred million years in ours. She celebrated her 45th birthday about six months ago, and she can reasonably expect to live for another half-century.
For Dr. Earth, the Bush administration is a but a blink of the eye — about 2.5 seconds. Our country declared independence about 73 seconds ago. The last ice age ended about an hour ago — 11,000 years ago in real time. Our species isn’t quite a day old (250,000 real years), and we shared an ancestor with chimpanzees about four weeks ago — 8 million years ago in real time. The dinosaurs, which first appeared about two years ago, died out about eight months ago (65 million years of real time). And there were still nearly 45 years of Dr. Earth’s life before that.
So taking our first tentative step into deep time, let’s look at Earth’s last million years, the last four days of Dr. Earth’s life. For the last million years, the Earth has alternated between long glacial intervals and shorter interglacial intervals. We’re in an interglacial now; the one before that was about 125,000 years ago, and the one before that about 200,000 years ago. The pace of these changes is set by changes in where sunlight falls on the Earth, controlled by factors like the tilt of Earth’s axis and the eccentricity of Earth’s orbit. Variations in these astronomical parameters occur in cycles of 22 thousand years, 41 thousand years, and 100 thousand years, and these interact to put the Earth in and out of glacial stages.
During the peak of the last ice age, about twenty thousand years, carbon dioxide levels were about around 200 ppm (a bit more than half of what they are today) and global temperatures were about 5° F colder than they are today. An ice sheet miles thick extended so far south it covered Minnesota, Michigan, New York, and Massachusetts in North America; another ice sheet extended from Scandinavia into Britain, Denmark, and Poland.
That’s 5° F for you.
Let’s step back once more and cast our glance over the last few years of Dr. Earth’s life. Over timescales of many millions of years, climate seems to be controlled by carbon dioxide responding to the pacemaker of plate tectonics. Weathering takes granite from mountains, dissolves it, and carries it to the oceans, where it reacts with carbon dioxide to form limestone, which removes the carbon dioxide from the atmosphere. So when continents are colliding with each other and uplifting mountains, carbon dioxide levels go down and the planet cools. When continents are splitting from one another, and mountains are less steep, carbon dioxide levels rise. Over many tens of millions of years, the Earth breathes, alternating between Hothouse climates where ice sheets are small or absent, and Icehouse climates with large polar ice sheets, as we have today.
The planet has been gradually cooling for about the last 45 million years, due in large part to the collision of India with Asia. So if we go back in time about three million years, we can find interglacial periods where the planet was about 5° F warmer than today, just as we expect if we cap carbon dioxide levels around 550 ppm. In this world, ice sheets could melt enough to produce sea levels 20 meters higher than today.
Looking over the broad sweep of Hothouse and Icehouse cycles, we find that ice sheets do not exist stably on the planet when carbon dioxide levels exceed 1000 ppm — levels we’ll reach by early in the 22nd century if we do nothing. The ice sheets would not collapse immediately, but over time scales we have difficulty predicting — perhaps centuries — they would disappear. Sea level on this planet with the Greenland, West Antarctic, and East Antarctic Ice Sheets all gone would be about 260 feet higher than today. Fifty million years ago, in a world like that, two-thirds of my state, New Jersey, was submerged in the ocean. Crocodiles roamed around the Arctic Circle.
That’s not a world we’re going to live in, nor is it a world we have to condemn our descendants to live in. But the decisions we make today shape our future as well as our descendants’ future. We are taking fossil fuels that have been buried in sedimentary rocks for tens of millions of years and rapidly burning them to release their carbon into the atmosphere. Most of the carbon dioxide we are putting into the atmosphere will stay up there for around 300 years, but about a quarter will stay up there for a thousand years, and around a tenth for 100 thousand years. We are acting as a geological force, transferring carbon from rocks into the atmosphere and ocean, and we are reshaping our world.
Our actions have consequences. Under a 550 ppm scenario, the climate of Massachusetts will by century’s end be like that of Washington, DC, today, with about 30 days a year in excess of 90° F; under a higher scenario, it will be more like that of South Carolina, with more than 60 days a year in excess of 90° F. Already, in the Northeast, warming temperatures are reducing snow pack and increasing the likelihood of extreme heat days.
Warming will affect agriculture: even under a 550 ppm scenario, cranberry crops in New Jersey are unlikely to survive. Cod fisheries will shrink, and lobster fisheries will migrate north. Under a high-end scenario, New England’s beautiful maple forests will largely give way to oak and hickory.
Under both a 550 ppm scenario and a high-end scenario, we will experience significant sea level change. In Boston, that means the current 100-year flood zone will become a near-annual flood zone, a change that will necessitate expensive infrastructure to protect the city, and ought to be motivating land use changes now.
We need to start acting now to mitigate our heat-trapping emissions, and we need to start planning now to adapt to changes that we will have difficulty avoiding. In 2004, the world emitted 30 billion tons of carbon dioxide to the atmosphere by burning fossil fuels. To stabilize carbon dioxide levels at 450 ppm, total emissions need to be cut by about 50% by 2050. But that’s a global target; as Americans, we have greater responsibility. 30 Gt is 4.6 tons for each person alive today. Our 2050 target is 1.7 tons per person for a population of 9 billion. In 2004, the US accounted for one-fifth of global emissions, and on average, each one of us emitted 20.5 tons of C. So to make the 450 ppm stabilization target, we need to cut our per capita emissions by about 90% over the next four decades.
There are some easy solutions that will get us part way. Due in large part to energy efficiency efforts that began in the 1970s, the average Californian emits about half that the average American. The average western European emits 40% that of the average American, and I’d wager most Europeans right now are happier with their lifestyle than we are with ours. The average New York City resident, by the way, emits about a third of what the average American emits.
The most important part of the solution is to put a price on carbon, either through a tax or by capping annual emissions through a cap-and-trade permit system. This price probably needs to be somewhere between $30 and $100 per ton. The advantage of an emissions trading scheme over a tax is that the market can figure out more precisely where it needs to be. The Northeast is instituting a regional cap-and-trade system for the electricity sector, RGGI, to begin in 2009. We need an all-sector, nationwide carbon pricing system in order to get on a stabilization scenario; there is legislation in pending in Congress, the Lieberman-Warner Climate Security Act, which doesn’t go quite far enough in terms of targets but does set up the trading infrastructure.
In Your Business
In your business, one of the most important first steps you can take is keep good carbon books. Life cycle analysis studies help estimate what the cost of a given product or action is over its entire economic life. It is through life cycle analysis, for instance, you can recognize that the energy put into growing corn for ethanol more than cancels out any emissions saving. With biofuels, for instance, you need to think about land use — where are people going to grow the crops? in newly deforested land? — and the energy emissions associated with things like fertilizer and the actual labor of growing and harvesting crops and transforming them into fuel. In general, when building infrastructure, we need to think of the long view: what will be the impact of a new building or new power plant over the next fifty years?
We also need to prepare to deal with 5° F warming we’re likely to face even if we stabilize carbon dioxide levels at 450 ppm. Two to three feet of sea-level rise this century is probably unavoidable; as a consequence, as I mentioned, the current one-hundred year flood zone in Boston will become the one-to-two year flood zone. The city will need to build flood barriers to protect landmarks like the Haymarket T Station and Quincy Market from near-annual flooding, and the state will need to protect vulnerable populations in places like Cape Cod. Sewer systems will need to be able to deal with the increased flooding. Our communities need to be prepared with the effects of recurring floods and heat waves; another Katrina is not acceptable.
Pale Blue Dot
I want to close by recalling an image popularized by the late Carl Sagan. In 1990, the Voyager 1 spacecraft, traveling on its way to the edge of the solar system, looked back at the Earth from 4 billion miles away — 43 times the distance from the Earth to the Sun. The entire Earth at that distance was visible as a single blue pixel.
“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives,” Sagan wrote. That’s our home, and we have now become one of the great forces that shape it. The question is whether we will use that power with rashness or with wisdom. The answer is up to every one of us.
For further reading, please see the Northeast Climate Impact Assessment.
“Carbon dioxide levels were around 280 ppm 250 years ago; right now, they’re at 380 ppm. Without action, we’re on track for 900 ppm by the end of the century and a warming of 7–11° F.”
“Fifty million years ago, in a world like that, two-thirds of New Jersey, was submerged in the ocean. Crocodiles roamed the Arctic Circle.”
“In Boston, that means the 100-year flood zone will become a near-annual flood zone, a change that will necessitate expensive infrastructure to protect the city, and ought to be motivating land use changes now.”
“As Americans, we have greater responsibility. In 2004, the US accounted for one-fifth of global emissions. So to make the 450 ppm stabilization target, we need to cut our per capita emissions by 90% over the next four decades.”