Ecology - The Great Climate Experiment / Ken Caldera

How far can we push the earth into a corner?

Business, government, or technology forecasts usually look five or ten years ahead, and fifty years at most. Climate scientists are even talking a little about the end of the century. But in reality, the carbon dioxide emitted into the atmosphere today will affect the planet for hundreds of thousands of years.

How will greenhouse gases change the distant future? No one can say for sure how the Earth will react to them. But climate scientists can predict with mathematical models what the world will look like. They build these models based on knowledge of the climate systems that prevailed in the past and knowledge of the complicated process network that affects the climate and based on the laws of physics and chemistry.

We are already seeing the realization of the future predicted by many of these models. As predicted, the surface of the earth warms more than the oceans, the poles more than the equator, the winters more than the summers and the nights more than the days. Extremely heavy rains have become more common. In the Arctic, the ice and snow cover less area and the methane-rich lands, which were frozen all year round, begin to thaw. The weather is getting weird, accompanied by storms caused by the excess heat.

What are the final limits of the change we generate? The best historical example comes from the climate during the Cretaceous period, which occurred 100 million years ago. At that time, hot and humid air enveloped the scaly skin of the dinosaurs, crocodile-like creatures that lived in the sea in the polar regions, and vegetation thrived in the carbon dioxide-rich air. The greenhouse conditions created now will have an effect for hundreds of thousands of years and more. But before that, they will have a profound effect on life on our planet - and especially on us.

Speaking in Italy
One of the biggest uncertainties in climate prediction is the amount of CO2 that will eventually be emitted into the atmosphere. In this article, I will assume that industrial culture will continue to do what it has done for the past 200 years. That is, it will burn mineral fuels at an increasing rate, until it is no longer economically profitable to extract them from the ground.

How much CO2 can we even release? In total there are about one million billion tons (1021 grams) of organic carbon trapped in some form in the Earth's sedimentary rocks. So far we have burned only 20th of 1% of this carbon, which means we have emitted about 2,000 billion tons of CO2.

Considering the total amount of carbon trapped in the Earth's crust, we will never exhaust all fossil fuels. Today we are extracting tar sands to produce crude oil and cracking oil shale using high pressure water to produce natural gas, two sources that in the past believed that it was technologically impossible to produce fuel from them and that this was not economically viable. No one can predict with certainty how far we can go with ingenuity and brilliant ideas. However, eventually the price of production and processing will reach a level where the mineral fuels will be more expensive than the alternative sources. According to the scenario in this article, we will eventually burn about 1% of the available organic carbon over the next few centuries. This estimate is based on the most logical level of production that we can achieve technologically in the foreseeable future. We also hypothesize that in the future humanity will learn to produce unconventional mineral fuels, but it will burn them at rates lower than the rates accepted today.

If we don't change our habits, the temperature on Earth is expected to increase by about 5 degrees Celsius by 2100, although the actual warming could be half that or even double that, mainly depending on the influence of clouds. This change is similar to the difference between the average climate in Boston, Massachusetts, and that of Huntsville, Alabama.

In the middle northern latitudes, between 30 and 60 degrees north, a strip that includes the USA, Europe, China and most of Canada and Russia [and also Israel - the editors], the average annual temperature decreases by 2 degrees Celsius for every one degree increase northward in the lines the width A warming of 5 degrees in a hundred years therefore translates into a northward movement of the temperature by an average of 800 kilometers, or an approach to the pole of the temperature strip by more than 20 meters every day. Squirrels might be able to keep up with that pace, but oak trees and sedges might have a hard time moving that fast.

Then the rains will come. Earth is a heat machine on a planetary scale. The sun heats the air in the equatorial region and it rises and cools. The cooling condenses water vapor in the air and the water returns and falls to the ground as rain. This is the reason for the band of torrential rains near the equator.
But this condensation also heats the air around it and makes it rise even faster. This hot and dry air reaches the height where jet planes fly and it spreads sideways, on both sides of the equator, towards the poles. The hot air at these heights emits the heat radiation into space, cools and descends back to the surface. The sun's rays penetrate through this dry, cloudless air and strike the arid surface. Nowadays, the dry air sinks approximately at latitudes 30 north and 30 south and forms the large desert strip that surrounds the earth [in Israel, the 30 north latitude runs about 50 kilometers north of Eilat - the editors].

Due to the warming caused by the greenhouse effect, the rising air is warmer. Therefore, it takes more time to cool and sink back to the surface, and the desert strips therefore move towards the poles.

Sahara desert climate may move north. Southern Europe is already experiencing years of extreme drought even though global precipitation is increasing. The region may lose the Mediterranean climate that has long been considered the most pleasant climate in the world. Instead, future generations may say this about the Scandinavian climate.

Further north in the middle latitudes, the growing seasons get longer. Spring is springing earlier: plants are blooming, the ice on the lakes is melting and the migratory birds are arriving earlier than ever before in recent history.

But these are not the only things that will benefit the crop fields in Canada and Siberia. Plants create food by utilizing the energy of sunlight to fuse CO2 and water. For the most part, the plants absorb CO2 through small pores on the leaves, called pionae. When the stomata are wide open, the plants are able to absorb a lot of CO2, but at the same time a lot of water evaporates through these gaping pores. If the concentrations of CO2 in the atmosphere are higher, the plants will be able to get the CO2 they need even when the leaves are only partially open, or they will be able to grow leaves that contain fewer leaves. In a high CO2 world plants can grow more with the same amount of water. (This decrease in evaporation will also result in a decrease in the amount of precipitation. Moreover, since evaporation cools, a decrease in its volume will result in further warming.)

But these improved conditions will not be felt everywhere. In the tropics, the high temperatures are damaging many crops already, and the heat wave will probably worsen with global warming. It seems that, overall, an increase in agricultural productivity is expected, because the increase in the north will exceed the decrease in the equatorial region. Global warming may not reduce the overall food supply, but it may give more to the rich and less to the poor.

Oceans of change
The vast oceans resist change, but they will change nonetheless. Scientists predict that in the coming decades the chemistry of the oceans will change to a greater extent and at a faster rate than it has ever changed, except perhaps during the mass extinction events. When CO2 molecules enter the sea they react with the water and form carbonic acid. In high enough concentrations, this acid can dissolve the shells and skeletons of many marine animals, especially those made of the more soluble form of calcium carbonate, called aragonite.

Scientists estimate that more than a quarter of all marine species spend part of their lives on coral reefs. The coral skeletons are made of aragonite. And even if the chemical conditions do not deteriorate to the point where the clams and shells dissolve completely, the increase in water acidity may make it difficult for these animals to build them. In just a few decades there will be no places left in the oceans where the chemical conditions prevail that in the geological past supported the growth of coral reefs. It is not known how many species that depend on corals will disappear along with the reefs.

Such chemical changes will most directly affect reef life, but the rest of us should consider the physical changes that are about to occur. At the most basic level, water behaves like mercury in a thermometer: if you raise the temperature, you'll see the mercury rise. And in addition to that, water trapped today in the ice caps at the poles feeds the sea.

In the distant past, at times when the level of CO2 was high, the Earth warmed enough to sustain crocodile-like animals north of the Arctic Circle. About 100 million years ago the average annual temperature at the pole reached 14 degrees Celsius. At the height of summer, temperatures rose above 25 degrees. Such temperatures over thousands of years will melt the ice covering Greenland and Antarctica. If the ice melts completely, the sea level will rise by 120 meters and flood large areas. The weight of the water over the continental lowlands will push them down, deep into the Earth's crust, causing the water to rise even more.

The poles are expected to warm at a rate 2.5 times higher than that of the entire Earth. Already, the Arctic has warmed faster than any other region, by about 2 degrees Celsius compared to the global average of 0.8 degrees. At the end of the last ice age, when the climate warmed by about 5 degrees Celsius for several thousand years, the ice caps melted at a rate that caused the sea level to rise by about one meter every hundred years. We hope and expect that the ice will not melt at a faster rate, but we are not convinced.

chase Venus
Over the past several million years, Earth's climate has fluctuated, causing the large ice sheets to expand and contract. But our greenhouse gas emissions hit this complex system like a bat. So far I have presented a scenario where our climate evolves quite smoothly. But there may also be jumps and leaps that may undermine biological, social and political systems and cause them to exceed their endurance limits.

Consider, for example, the possibility that Arctic warming will cause hundreds of billions of tons of methane gas to rapidly bubble up into the atmosphere from the Arctic seabed and the thawing frozen lands. A methane molecule is about 37 times more efficient at trapping heat than a CO2 molecule. And if the methane is released all at once, as probably happened in the peak warming event 55 million years ago, in the transition between the Paleocene and Eocene eras, we are expected to experience truly catastrophic warming. But most scientists believe that the chance of this is small.

Some have also proposed a scenario in which feedback loops, such as the effect of the melting of the witness glaciers, will cause an increasing acceleration of the greenhouse effect until the oceans warm up and evaporate completely. Water vapor is also a greenhouse gas, therefore, such an extended water cycle will warm the Earth to such an extent that the water vapor will remain in the atmosphere and never condense into rain. In that case, CO2 released from volcanoes and other sources will also continue to accumulate. Cosmic radiation is able to break a water molecule at high altitude and the hydrogen that will be formed will eventually escape into space. The Earth's climate may then stabilize in a situation similar to that prevailing on the neighboring planet, Venus.

Fortunately, there is almost no chance that today's greenhouse gas emissions will cause the oceans to evaporate. Simply put, there is a limit to how much CO2 can warm our planet. As soon as the concentrations of CO2 and water vapor reach a high enough level, the molecules scatter the sunlight that falls on them to an increasing extent and prevent further warming.

However, if we continue to burn fossil fuels, the concentrations of greenhouse gases in the atmosphere will reach levels last seen only in the Cretaceous era. The hot and humid Earth of that time had large areas flooded by inland seas. On land, dinosaurs grazed the lush vegetation. If we burn only 1% of all the organic carbon found in the Earth's crust over the next few hundred years, humans will inhale CO2 in the same concentrations as the dinosaurs and will experience similar temperatures.

Compared to the gradual warming that characterized greenhouse climates in the past, industrial climate change is occurring at a murderous pace. Throughout geologic history, transitions from CO2-poor to CO0.00001-rich atmospheres have generally occurred at rates resulting in warming of less than 5,000 degrees Celsius per year. We are recreating the world of dinosaurs at a rate XNUMX times faster.

What will thrive in this greenhouse? Some creatures, such as rats and cockroaches, are versatile invaders capable of taking advantage of disturbed environments. Others, such as corals and many tropical forest species, have evolved during evolution only in a way that allows them to thrive in a narrow range of conditions. It is likely that as a result of global warming, invasive species will change the face of such ecological environments. Climate change may lead to a world of weeds.

Human civilization is also in danger. Remember the Mayans in Central America. Even before the arrival of the Europeans, the Mayan culture began to collapse following a relatively mild climate change. The Mayans did not develop enough flexibility to deal with a slight decrease in rainfall. And the Maya are not the only example of a culture that failed to adapt to climate change.

It is likely that the crises that climate change will bring will be regional crises. If the rich get even richer, and the poor get poorer, will this lead to a large migration of peoples that will undermine political and economic stability? Some of the countries most likely to be affected by global warming possess nuclear weapons. Could climate change increase existing tensions and trigger nuclear conflicts, or other apocalyptic scenarios? The social response to climate change may produce more serious problems than the climate change itself.

start again
The luxuriant plants that thrived during the Cretaceous died out. In the course of geological time, some of them were turned into coal. The plankton in the ocean was buried in the sedimentary rocks and some of it became oil and gas. Sea life trapped CO2 in oysters and skeletons and the climate cooled.

Over thousands of years the sea will absorb most of our CO2. The increase in water acidity that will occur due to this will cause carbonate minerals to dissolve and the chemical effect of the dissolution will allow the water to absorb more CO2. And yet, for tens of thousands of years, CO2 concentrations in the atmosphere will remain well above 280 parts per million, their pre-industrial level. As a result, the tidal fluctuations of the ice ages caused by slight changes in the Earth's orbit will stop, and the greenhouse gases emitted by humans will trap the planet in a greenhouse.

Over time, the high temperatures and increased precipitation will accelerate the rate of dissolution of rocks and soil. Streams and rivers will carry the dissolved rocks and minerals, containing elements such as calcium and magnesium, to the sea. Perhaps in hundreds of thousands of years some marine creature will capture the calcium and the carbon dioxide and build a carbonated clam for itself. This clam, along with millions of similar creatures, eventually formed limestone. Just as the White Cliffs of Dover in England are a remnant of the cratonic atmosphere, so too will most of the carbon found in the fossil fuels burned today be collected in a layer of rock - evidence, written in stone, of a world that has undergone change because of one and only biological species.

About the author

Ken Caldeira is a climate scientist at the Carnegie Institution for Science in the Department of Global Ecology at Stanford University. He researches issues related to climate, carbon and energy systems. His main research tool is climate and carbon cycle models. He also conducts field research related to the increasing acidity of the oceans.
Fast forward

Climate: past and future
Assuming that we continue to burn fossil fuels as we please and that we continuously release greenhouse gases, such as carbon dioxide, into the atmosphere, our planet will change its face. Already now, temperatures in the world have risen on average by almost one degree Celsius, and at a rate twice that in the polar regions. Eventually, temperatures could rise by 10 degrees Celsius, enough warming to melt the vast amounts of water now stored in Greenland and Antarctica's glaciers. As a result, enough water will be released to raise the sea level by 120 meters. Atmospheric concentrations of carbon dioxide will reach levels last seen during the Cretaceous period, when dinosaurs ruled the land, when a vast inland basin split North America in two, and when crocodile-like creatures lived at the poles.
And more on the subject
Oceanography: Anthropogenic Carbon and Ocean pH. Ken Caldeira and Michael E. Wickett in Nature, Vol. 425, page 365; September 25, 2003.
Climate Change 2007: The Physical Science Basis. International Panel on Climate Change. Cambridge University Press, 2007. www.ipcc.ch/publications_and_ data/ar4/wg1/en/contents.html
The Long Thaw. David Archer. Princeton University Press, 2010.