Climate projections for the 21st century and climate change consequences and stabilization

Fresh water

·         Dry regions are projected to get drier, and wet regions are projected to get wetter: "By mid-century, annual average river runoff and water availability are projected to increase by 10–40% at high latitudes and in some wet tropical areas, and decrease by 10–30% over some dry regions at mid-latitudes and in the dry tropics..."

·         Drought-affected areas will become larger.

·         Heavy precipitation events are very likely to become more common and will increase flood risk.

·         Water supplies stored in glaciers and snow cover will be reduced over the course of the century.

 

Ecosystems

·         The resilience of many ecosystems is likely to be exceeded this century by a combination of climate change and other stressors.

·         Carbon removal by terrestrial ecosystems is likely to peak before mid-century and then weaken or reverse. This would amplify climate change.

Food

It is projected with medium confidence (about 5 in 10 chance to be correct) that globally, potential food production will increase for temperature rises of 1–3 °C, but decrease for higher temperature ranges.

Coastal systems

·         Coasts will be exposed to increasing risks such as coastal erosion due to climate change and sea-level rise.

·         "Increases in sea-surface temperature of about 1–3 °C are projected to result in more frequent coral bleaching events and widespread mortality unless there is thermal adaptation or acclimatisation by corals."

·         "Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s."

Observed and expected environmental effects

Projections of global mean sea level rise .

Natural systems

Global warming has been detected in a number of natural systems. Some of these changes are described in the section on observed temperature changes, e.g., sea level rise and widespread decreases in snow and ice extent. Anthropogenic forcing has likely contributed to some of the observed changes, including sea level rise, changes in climate extremes (such as the number of warm and cold days), declines in Arctic sea ice extent, and to glacier retreat

Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s measurements began that allow the monitoring of glacial mass balance, reported to theWorld Glacier Monitoring Service (WGMS) and the National Snow and Ice Data Center (NSIDC)

Over the 21st century, the IPCC projects that global mean sea level could rise by 0.18-0.59 m. The IPCC do not provide a best estimate of global mean sea level rise, and their upper estimate of 59 cm is not an upper-bound, i.e., global mean sea level could rise by more than 59 cm by 2100. The IPCC's projections are conservative, and may underestimate future sea level rise. Over the 21st century, Parris and others suggest that global mean sea level could rise by 0.2 to 2.0 m (0.7-6.6 ft), relative to mean sea level in 1992.

Widespread coastal flooding would be expected if several degrees of warming is sustained for millennia. For example, sustained global warming of more than 2 °C (relative to pre-industrial levels) could lead to eventual sea level rise of around 1 to 4 m due to thermal expansion of sea water and the melting of glaciers and small ice caps. Melting of the Greenland ice sheet could contribute an additional 4 to 7.5 m over many thousands of years.

Changes in regional climate are expected to include greater warming over land, with most warming at high northern latitudes, and least warming over the Southern Ocean and parts of the North Atlantic Ocean. During the 21st century, glaciers and snow cover are projected to continue their widespread retreat. Projections of declines in Arctic sea ice vary. Recent projections suggest that Arctic summers could be ice-free (defined as ice extent less than 1 million square km) as early as 2025-2030.

Future changes in precipitation are expected to follow existing trends, with reduced precipitation over subtropical land areas, and increased precipitation at subpolar latitudes and some equatorial regions. Projections suggest a probable increase in the frequency and severity of some extreme weather events, such as heat waves.

Ecological systems

In terrestrial ecosystems, the earlier timing of spring events, and poleward and upward shifts in plant and animal ranges, have been linked with high confidence to recent warming. Future climate change is expected to particularly affect certain ecosystems, including tundra, mangroves, and coral reefs. It is expected that most ecosystems will be affected by higher atmospheric CO₂ levels, combined with higher global temperatures. Overall, it is expected that climate change will result in the extinction of many species and reduced diversity of ecosystems.

Increases in atmospheric CO₂ concentrations have led to an increase in ocean acidity. Dissolved CO₂increases ocean acidity, which is measured by lower pH values. Between 1750 to 2000, surface-ocean pH has decreased by ~0.1, from ~8.2 to ~8.1. Surface-ocean pH has probably not been below ~8.1 during the past 2 million years. Projections suggest that surface-ocean pH could decrease by an additional 0.3-0.4 units by 2100. Future ocean acidification could threaten coral reefs, fisheries, protected species, and other natural resources of value to society.

Long-term effects

On the timescale of centuries to millennia, the magnitude of global warming will be determined primarily by anthropogenic CO₂ emissions. This is due to carbon dioxide's very long lifetime in the atmosphere.

Stabilizing global average temperature would require reductions in anthropogenic CO₂ emissions. Reductions in emissions of non-CO₂ anthropogenic GHGs (e.g., methane and nitrous oxide) would also be necessary. For CO₂, anthropogenic emissions would need to be reduced by more than 80% relative to their peak level. Even if this were to be achieved, global average temperatures would remain close to their highest level for many centuries.

Large-scale and abrupt impacts

Climate change could result in global, large-scale changes in natural and social systems. Two examples are ocean acidification caused by increased atmospheric concentrations of carbon dioxide, and the long-term melting of ice sheets, which contributes to sea level rise.

Some large-scale changes could occur abruptly, i.e., over a short time period, and might also be irreversible. An example of abrupt climate change is the rapid release of methane and carbon dioxide from permafrost, which would lead to amplified global warming. Scientific understanding of abrupt climate change is generally poor. However, the probability of abrupt changes appears to be very low. Factors that may increase the probability of abrupt climate change include higher magnitudes of global warming, warming that occurs more rapidly, and warming that is sustained over longer time periods.

Observed and expected effects on social systems

Vulnerability of human societies to climate change mainly lies in the effects of extreme weather events rather than gradual climate change. Impacts of climate change so far include adverse effects on small islands, adverse effects on indigenous populations in high-latitude areas, and small but discernable effects on human health. Over the 21st century, climate change is likely to adversely affect hundreds of millions of people through increased coastal flooding, reductions in water supplies, increased malnutrition and increased health impacts.

The economic impacts of climate change are highly uncertain. Small magnitudes of global warming (0 to 2 °C, relative to pre-industrial levels) could lead to losses or gains in world gross domestic product (GDP). Above around 2.5 °C, most studies suggest losses in world GDP, with greater losses at higher temperatures.

Food security

Maize field in South Africa

Under present trends, by 2030, maize production in Southern Africa could decrease by up to 30%, while rice, millet and maize in South Asia could decrease by up to 10%. By 2080, yields in developing countries could decrease by 10% to 25% on average while India could see a drop of 30% to 40%. By 2100, while the population of three billion is expected to double, rice and maize yields in the tropics are expected to decrease by 20–40% because of higher temperatures without accounting for the decrease in yields as a result of soil moisture and water supplies stressed by rising temperatures.

Future warming of around 3 °C (by 2100, relative to 1990–2000) could result in increased crop yields in mid- and high-latitude areas, but in low-latitude areas, yields could decline, increasing the risk of malnutrition. A similar regional pattern of net benefits and costs could occur for economic (market-sector) effects. Warming above 3 °C could result in crop yields falling in temperate regions, leading to a reduction in global food production.

Habitat inundation

_{Map showing where natural disasters caused/aggravated by global warming may occur.}

In small islands and megadeltas, inundation as a result of sea level rise is expected to threaten vital infrastructure and human settlements. This could lead to issues of homelessness in countries with low lying areas such as Bangladesh, as well as statelessness for populations in countries such as the Maldives and Tuvalu.

Stabilization Wedge Game

The Stabilization Wedge Game, or what is commonly referred to as simply the 'Wedge Game', is a serious game produced by Princeton University's Carbon Mitigation Initiative. The goal of the game creators, Stephen Pacala and Robert H. Socolow, is to demonstrate that global warming is a problem which can be attacked right now by using today's technologies to reduce  CO
2 emissions. The object of the game is to stabilize CO
2 concentrations under 500ppm for the next fifty years, using seven wedges from a variety of different strategies which fit into the stabilization triangle. A new estimate by the original authors indicates that 9 wedges are now necessary, as emissions have continued to rise since the original paper on which the game was based was published

Concept

Scenario

Emissions of CO2 and other greenhouse gases have been increasing ever since the Industrial Revolution, and if the world continues business as usual, emissions will double by 2055. To prevent the worst consequences of global warming, scientists recommend freezing and reducing net global emissions immediately.

Stabilization triangle

If global emissions of CO2 are graphed for the next 50 years, the difference between the business as usual scenario and the flat path forms a triangle. This triangle is known as the stabilization triangle. Pacala and Socolow divided this hypothetical triangle into seven stabilization wedges, which represent different measures that must be taken to reduce emissions. When speaking of different strategies to reduce emissions, the language "to reduce one wedge's worth," is often employed, and by reducing the stabilization wedge of fourteen gigatons of CO2 into seven wedges, the task is much easier to conceptualize.

Wedge strategies

As Pacala and Socolow originally presented the wedges concept in Science, there are fifteen different wedge strategies. Regarding the specific number, Socolow says that he and Pacala didn't include all of the possibilities, but that "It was a matter of rhetoric to stop at 15. And exhaustion. There was nothing magic about 15." On the CMI website, the same strategies are presented and expanded upon in detail, and are re-organized into four categories:

1.     Efficiency (4 strategies)

2.     Decarbonization of power (5 strategies)

3.     Decarbonization of fuel (4 strategies)

4.     Forest and agricultural soils (2 strategies)

Uses

An example of a self-made Wedge Game board used by the Houston Advanced Research Center

Because of the simplicity of the wedge game, it has become popular as a communication tool for global warming mitigation. It is used in a variety of arenas and by a variety of players including businessmen, politicians, teachers, and students. David Hawkins, climate director at the Natural Resources Defense Council, puts the ease of use of the Wedge Game this way:

“

The wedges concept is sort of the iPod of climate policy analysis... It's an understandable, attractive package that people can fill with their own content."

”

Education

The Carbon Mitigation Initiative (CMI) permits anyone to use the game and make use of their materials, provided that they share the results with CMI. Because it is so widely accessible, it has become included in certain high school curricula. The Keystone Center has deemed the Stabilization Wedge Game to fulfill the following National Education Standards: S1, S6, LA4, LA5, C4, C5, E1, G1, G5, and WH9

The American Association for the Advancement of Science hosted a conference for educators at the Hilton inSan Francisco 2007-02-18. Collaborating with AAAS were the National Science Teachers Association and theUnited Educators of San Francisco (representing the National Education Association and the American Federation of Teachers). Dr. Socolow and Dr. Hotinski personally presented the Stabilization Wedge concept at the event.

Business

The Stabilization Wedge Game is also used as a centerpiece for business seminars. Business executives played the game at as seminar held by the Sustainable Enterprise Academy at York University in Toronto.

Criticism

The primary critique of the Wedge Game is that it is too simple, especially regarding the economic aspect of global warming mitigation. The materials provided by CMI only attach one, two, or three dollar signs to each wedge as a broad estimate of the expense of each option. James L. Connaughton, former chairman of the White House Council on Environmental Quality in the Bush Administration, is a critic of the Wedge Game for its oversimplicity, and he has even said that some of the numbers used by Socolow and Pacala, such as 550 ppm as a maximum allowable target for CO
2, lack a scientific basis. Richard G. Richels, a senior engineer at the Electric Power Research Institute, says that the lack of economic precision in the game could create misconceptions:

“

We have to find out what it's going to cost to make it affordable. By not including the cost issue, people come away from this thinking it will be a piece of cake. It's going to require some serious bucks. If the environment is priceless, we should be willing to pay some serious bucks to protect it.

”

Another criticism of the game is that one of the premises, i.e. that humanity already has the tools and technologies to halt climate change, is misleading. Marty Hoffert of the New York University Physics Department claims that while the technologies are available in a technical sense, they are not available in an operational sense, and it will take a massive mobilization to make progress. Hoffert explains:

“

...humanity had the know-how to build nuclear weapons in the late 30s or go to the Moon in the 60s. But it took the Manhattan and Apollo programs to make it so...An Apollo-like program in alternate energy is needed over a broad spectrum of mitigation technologies.

”

In a 2010 Science article, Hoffert also suggested that 18-25 wedges may be necessary to achieve the goal, given the higher rates of emission growth that have occurred since the original study, even if no new sources were added beginning in 2010.

In June 2008, Joseph Romm argued in Nature magazine that "If we are to have confidence in our ability to stabilize carbon dioxide levels below 450 p.p.m. emissions must average less than 5 GtC per year over the century. This means accelerating the deployment of the... wedges so they begin to take effect in 2015 and are completely operational in much less time than originally modelled by Socolow and Pacala."

A final criticism is that the Wedge Game focuses on technological fixes rather than fundamentally challenging the endless growth economy that is at the heart of global climate change. The 2007 IPCC reports state clearly that economic and demographic growth are the fundamental drivers of global climate change. Yet of the fifteen wedges developed by Pacala and Socolow, only one—halving the number of miles driven by the world's automobile fleet—might be considered a "demand reduction" wedge. None of their wedges treat population reduction.