Why Now?

Feedbacks, tipping points, and energy

If we’ve put off action for decades, what difference would a few more years make? There are basically three reasons: both global energy demand and the climate system have built up so much momentum that it will be difficult to stop either, and we need to act now to preserve energy security.

“It will all work out”

Even if we were to find the solutions to all of our problems, the composition of the atmosphere would not return to normal under any reasonable time scale. As we’ve discussed, much of the emitted CO2 stays in the atmosphere for centuries or longer so there can be no quick fix to this problem (see section 7). In addition, we’ve locked ourselves into about 0.5 ° of additional warming even if all of civilization were to cease tomorrow.[1] This is the amount of warming required before the ocean reaches its new equilibrium. If we remember the beaver dam metaphor from section 1, we’ve built up the dam (greenhouse gases) so quickly that the pond (trapped energy) will continue to rise even after we stop building. Furthermore, we cannot turn on a dime. It will take a decade or two to slow and then reverse the growth of emissions as fossil fuels are replaced with renewable energy. The bottom line is that we will experience about 1 ° of additional warming no matter what we do.


There are several feedbacks that make the problem worse, potentially making it impossible to avert dangerous climate change.

The most obvious is melting arctic ice, called the “ice albedo feedback.” As ice melts it is replaced by open water. Water is darker and thus absorbs more energy than the white ice. As a result, the arctic is being transformed from a reflector of energy to an absorber which increases the melting.

Another feedback is the potential release of methane from natural stores. With the proper conditions, methane and water combine to form ice-like methane clathrates, also known as hydrates. There are hundreds of gigatons of methane locked away in permafrost, and as more of it melts during the summer, the clathrates will melt along with it, releasing the methane.

There is an even greater amount of methane stored in sediments on continental shelves. As the ocean warms to greater depths, the clathrates could melt, and methane would bubble to the surface. This isn’t expected to happen for millennia because it takes such a long time for heat to sink to deeper waters. However, we may commit the ocean to the required warming much sooner than that. Methane is about 20 times more powerful than CO2 so a substantial release from permafrost or sediments would be catastrophic for any civilization living at that time.

Further feedbacks come about with changes to the carbon cycle.

With additional CO2 in the air, vegetation generally absorbs more, creating a negative feedback. However, as temperature and precipitation increase, this effect is reduced and then reversed. Eventually the soil will become a net emitter of CO2.

Another change is the disruption of the world’s forests, such as the drying of the Amazon. Shifting precipitation and increased deforestation replaces the rainforest with savannah. Rainforests themselves influence precipitation. As they shrink, precipitation decreases, causing more of the forest to die in a reinforcing cycle. The carbon contained within the forests is released into the atmosphere as CO2. Also at risk are boreal forests, which are the thick coniferous forests that exist throughout Canada, Alaska, Scandinavia and Siberia. Changes in precipitation, increased fire and disease, and permafrost melt cause the forests to be replaced with grasslands and open woodlands.

Finally are the expected changes to ocean chemistry. Ocean currents are driven by wind on the surface, and density changes due to temperature and salinity, which is known as the thermohaline circulation or ocean conveyor belt. This is expected to slow down due in part to the freshening of the North Atlantic. When a current plunges from the surface into the deep ocean, it transports dissolved CO2 along with it. Any reduction in the overturning of the ocean would increase the amount of CO2 that remains in the atmosphere. In addition, the more CO2 the upper ocean absorbs, the harder it is to absorb more. The ocean’s ability to “buffer” this CO2 is decreased.

Carbon cycle feedbacks such as these add up to 1.5 ° of additional warming by the year 2100 in the IPCC’s more pessimistic scenarios.[2]

Tipping points[3]

Often related to feedbacks are tipping points. The graphic summarizes the work of 36 scientists who participated in a recent workshop on tipping points. Each shaded area has its own tipping point, or a threshold that, once passed, causes an irreversible transition to a new state. All of this is highly uncertain so the temperatures and timespans given here must be taken with a grain of salt. However, the possibility of breaching just one of these tipping points is reason enough to act. For simplicity, the temperature rise given refers to the change over the globe. The local temperature change for each area will be different. Please note that the “transition time” is the amount of time it will take to transition to the new state after the tipping point is breached. It is not the amount of time until the tipping point is breached.

Why Now?

The first two tipping points are of immediate concern, because they may be breached under even the most aggressive greenhouse gas abatement policies.

Uncertainty cuts both ways

Talk of the future obviously includes great uncertainties, even as our understanding of the climate increases. However, when scientists make projections into the future, we often think about uncertainty as it relates to overestimating danger. But uncertainty exists in both directions, and prominent examples are the past estimates of sea level rise. The IPCC’s Third Assessment Report (TAR) from 2001 presented a range of future scenarios from the base year of 1990, but reality has followed the worst case scenario, boxed in green below.[4]

Antarctica is losing ice (but shouldn’t be)

The discrepancy between expected and actual sea level rise is partly explained by the way computer models treat Antarctica. All of the studies of Antarctica summarized in AR4 show it to be currently losing ice (see last section). Yet, every future scenario in AR4’s table expects the thickening of East Antarctica to reduce sea level rise and the loss from Greenland to be a minor contributor.[5]

Since these scenarios summarize changes by the end of the 21st Century, perhaps this is a temporary loss of ice, and the mass balance will become more favorable as time goes on. However this is implausible given past instances of sea level rise after similar temperature increases, such as that seen during the last interglacial period. Regardless, much work is going into the next generation of models to better describe the flow of ice sheets.

2007 Arctic Sea Ice was 50 years ahead of schedule

Also on the topic of how little we understand ice, another large shortcoming of the IPCC projections is their treatment of Arctic sea ice. Not only have recent conditions blown past the average scenario, we’ve even outpaced the worst case scenario.[6]

The result is that we have reached conditions in 2007 that were not projected to happen until around 2060. The worst case scenario did not foresee current conditions until about 2030. Referring back to our discussion of the polar bear, the committed extinction by the mid to late 21st century has now been moved to the immediate future, unless there is a rapid turnaround of Arctic ice.

Is this what a tipping point looks like? [7]

We mentioned that Arctic sea ice may have already tipped, and this is why.

The graphic shows the average amount of perennial sea ice during February from 1985 to 2000, with purple showing ice 6 years or older and red showing ice less than one year old. The graphic on the right shows the age of the ice as of February 2008. The new ice is both thinner and more salty than the old ice it replaced and will melt that much easier by late summer. It’s possible that it might recover if conditions in coming years are favorable, and the perennial ice is rebuilt. Otherwise, we may be heading for a permanent reduction in summer sea ice.

Energy demand

The other reason why immediate action is required is due to our energy situation.

Demand is rising exponentially due to population increase and increasing affluence, especially in developing nations such as China and India.[8]

“Peak oil”

Of all the forms of energy that we rely on, oil is the hardest to replace, and its supply is limited. We pump the easiest oil first, and as those sources are exhausted, we turn to more exotic and therefore more expensive sources. Eventually, it becomes so difficult to extract that production peaks and then declines.

In the United States, oil production peaked in 1970.

As domestic production declines, imports have made up the difference.[9] Despite the additional oil production from Alaska and the Gulf of Mexico, domestic production continued to drop. This was not due to lack of drilling.

In the early ‘80s, the number of oil wells drilled increased fourfold, yet domestic oil production never reached the peak set in 1970. As certainly as the United States peaked, the rest of the world will as well, the only question is when.

Numerous studies have been conducted on the timing of a peak in global oil production. Most of these studies project that world oil production will peak sometime between right now and 2040.[10]

Even if production doesn’t peak until 2040, it still requires decades to transition from existing infrastructure to whatever replaces oil, so the time to start is now.

Oil reserves are tenuous[11]

The reason it is so difficult to estimate the timing of peak oil is due to the fact that the vast majority of known reserves are controlled by foreign nations. Because the reserves are not controlled by publicly traded companies, they cannot be independently audited, so all we have to go on is the word of governments.

The white area above shows the proven reserves of the OPEC countries, with Saudi Arabia alone having as much oil as all of the non-OPEC countries put together. Another way to illustrate this is by the companies that actually produce the oil.

On the right shows the top 10 oil and gas companies in terms of the oil reserves that they hold, and only the Russian oil company Lukoil is a publicly held. On the left shows the top 10 companies not by the amount of oil they hold, but by production, and even then the public companies still can’t compare to the state run companies. What we do know is that most of the nations outside of the Middle East have already peaked. In addition, many of the nations with the largest reserves are in unstable parts of the world, or are unfriendly to the west. The combination of these factors shows just how dubious the world’s energy security really is.

Resource constraints may worsen the situation

In our rush to secure alternatives to oil, we may end up making global warming worse. There are three other fossil fuels from which we can make synthetic oil. The first is from oil sands, commonly called tar sands, almost of all of which are located in Alberta, Canada. This system is already up and running and the Canadians are investing many billions of dollars to expand production. The second is from coal. The United States has the largest coal reserves in the world, so this is particularly attractive to US policymakers. South Africa is already converting coal to liquids on a large scale. The third is from Oil Shale, almost all of which exists in Wyoming, Utah, and Colorado. To date, no one has demonstrated an economically feasible way of converting oil shale into oil.

All of these methods are extremely inefficient. So not only do we have to contend with the emissions from burning the fuels themselves, we have to deal with the emissions of the process to make the fuel. For example, in order to convert oil sands into oil, Canada is burning through its natural gas reserves.

The process that turns coal into liquids creates twice as much CO2 as does burning petroleum. Only with carbon capture and storage could emissions be comparable to the petroleum equivalent. For oil shale, the only proposed process would require dedicated power plants to operate an elaborate system to prep for and then carrying out the process.

In all cases, these methods are very destructive of the land, generating huge amounts of waste and requiring large amounts of water.

The false promise of (most) biofuels

Another proposed solution to our oil problems are biofuels. From a superficial standpoint, biofuels are supposed to be carbon neutral. That is, when they grow, they are supposed to take in just as much CO2 as they emit when they are burned, so their net contribution should be zero.

Studies that have looked into this issue show that most biofuels cause more emissions than they will ever be able to prevent. Many assumptions go into these studies so the exact numbers vary widely.

This study[12] calculates that converting peatland rainforest in Indonesia and Malaysia into palm oil plantations for biodiesel would require over 400 years to pay back the initial destruction of the rainforest. That is one of the reasons why Indonesia is already the third largest emitter of greenhouse gases behind China and the United States.

Corn ethanol replacing grassland in the United States takes over 90 years to pay back. Even replacing abandoned cropland, Corn Ethanol requires nearly 50 years to pay back.

Of the currently produced biofuels, only sugarcane ethanol has a reasonable payback of just 17 years. Future technologies such as cellulosic ethanol work out to be truly carbon neutral, provided that abandoned or marginal cropland is converted, and not natural environments.

In addition, growing crops for transportation puts more stress on available water and irrigation. Increasing oil prices drives up both the price of food and the demand for biofuels. Biofuels, in turn, compete for crops which further increases the price of food. After 30 years of decline, food prices are spiking upward. [13]

The last time the real price of food was this high, there were 2 billion less people in the world.

In the United States, corn is the biofuel we are most familiar with, and it is highly subsidized by the federal government. Its energy return is barely positive, about 25% more energy comes out than went in. If we converted the entire corn crop ethanol, it would reduce gas consumption by just 12%.[14]

Corn requires a lot of fertilizer, which is made with natural gas. A portion of the nitrogen in the fertilizer is eventually given off as nitrous oxide, which is about 300 times more powerful than CO2. In addition, fertilizer runoff enters the Mississippi river and eventually ends up in the Gulf of Mexico where it creates large algae blooms. After they die, the algae are decomposed by bacteria that suck the oxygen out of the water and kill everything else resulting in a dead zone roughly the size of New Jersey every year.[15]

The elephant in the room

The public tends to associate oil with global warming because that is what they are most familiar with when they fill up their cars. However, the real danger is not necessarily oil, which plays an important but limited role. The problem is our use of coal.

To illustrate this, we can create different emissions scenarios based on likely supplies of fossil fuels .[16]

Each line represents a different contribution to the CO2 concentration of the atmosphere: brown indicating coal, blue indicating oil, and green indicating natural gas. The red line represents all fossil fuel emissions combined, whereas the black line includes emissions due to land use changes. In the Business as Usual Scenario, we basically burn the fossil fuels until we run out of each of them, which puts us above 560 ppm and rising in 2100. All of the other scenarios assume that coal burning peaks in the next few years, and then we begin drawing down those emissions, either by replacing coal power plants with alternative energies or by capturing and then storing the CO2 underground. The various scenarios describe different ways to treat oil, but the point is that it is largely irrelevant what we do with our oil and natural gas, although it is still a good idea to conserve them for security reasons.

The generally accepted “safe limit” of CO2 is 450 ppm. The only way to prevent “dangerous anthropogenic interference” as mandated in the UN Framework Convention on Climate Change (see section 1) is to immediately freeze emissions from coal, reducing them shortly thereafter, and by avoiding unconventional sources of fossil fuels such as the oil shale and tar sands.


[1] (Hansen, et al., 2002) Online here.

[2] (Meehl, et al., 2007) Online here.

[3] (Lenton, Held, Kriegler, Hall, Lucht, & Schellnhuber, 2008) Online here.

[4] (Rahmstorf, et al., 2007) Online here.

[5] (Meehl, et al., 2007) Online here. Table 10.7.

[6] (Stroeve, et al., 2007) Online here.

[7] (Drobot, 2008) Online here.

[8] (Energy Information Administration, 2007) Online here. (US Census Bureau, 2008)

[9] (Energy Information Administration, 2008) Online here. (Energy Information Administration, 2008) Online here.

[10] (GAO, 2007) Online here.

[11] ibid

[12] (Fargione, Hill, Tilman, Polasky, & Hawthorne, 2008) Online here.

[13] (The Economist, 2007) Online here.

[14] (Hill, Nelson, Tilman, Polasky, & Tiffany, 2006) Online here.

[15] (NASA Goddard Space Flight Center, 2004) Online here.

[16] (Kharecha & Hansen, 2008) Online here. In press.

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