World Bank
Foreword
Scientists agree countries’ current … emission pledges and commitments would most likely result in 3.5 to 4°C warming. …
(p ix)
Executive Summary
A world in which warming reaches 4°C above preindustrial levels … would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on human systems, ecosystems, and associated services.
(p xiii)
Recent research suggests that large-scale loss of biodiversity is likely to occur in a 4°C world, with climate change and high CO2 concentration driving a transition of the Earth´s ecosystems into a state unknown in human experience.
(p xvi)
[Given the uncertainty] about the full nature and scale of impacts, there is … no certainty that adaptation to a 4°C world [would even be] possible.
A 4°C world is likely to be one in which communities, cities and countries would experience severe disruptions, damage, and dislocation …
It is likely that the poor will suffer most and the global community could become more fractured and unequal …
The projected 4°C warming … must not be allowed to occur …
[And only] early, cooperative, international actions can [prevent it.]
(p xviii)
Introduction
Current scientific evidence suggests that even with the current commitments and pledges fully implemented, there is roughly
- a 20% likelihood of exceeding 4°C by 2100, and
- a 10% chance of 4°C being exceeded as early as the 2070s. …
(Turn Down the Heat, World Bank, 2013)
Four Degrees and Beyond
Clive Hamilton: Professor of Public Ethics, Charles Sturt University
[In] late September 2009 [140 climate scientists gathered at Oxford University] to discuss the end of the world as we know it. …
IF
[Developed-country] emissions peak in 2015 and decline by 3% a year thereafter …
AND
[Developing-country] emissions peak in 2030 and decline 3% per year thereafter …
THEN
[The] world has a 50:50 chance of limiting warming to four degrees. …
{[And, since] the oceans warm more slowly, this means five to six degrees hotter on land.}
The biggest influences will be
- the rate of growth of the world economy, driven disproportionately by growth rates in China, India and Brazil, and
- the extent of efforts by governments in the major economies to restrain emissions. …
A planet four degrees warmer would be hotter than at any time since the Miocene era some 25 million years ago.
The world was virtually ice-free then. …
[During] the last interglacial or warm period 122,000 years ago [when temperatures were 1.5-2 degrees warmer] sea levels were ten metres higher than today. …
The record indicates that once the ice begins to melt it cannot be stopped …
[Beyond] two degrees the probability of the Greenland icesheet disintegrating is 50% or more, which would mean an additional rise of seven metres in sea levels over the next 300-1000 years [over an above that due to thermal expansion.]
Above two or three degrees the West Antarctic icesheet is also likely to disintegrate, adding another five metres to sea levels on top of this. …
[There are] 136 port cities with populations of a million or more [— most located in Asia. …]
It's expected that, overall, a warmer world will be more humid, with rainfall increasing by perhaps 25%. …
[However, the higher] rainfall will be concentrated in northerly latitudes, with large parts of the world nearer the tropics suffering a severe decline. …
[For example, projections for] Australia, southern Europe, western and central-southern United States … indicate precipitation declines of 10-30% in a four-degree world.
[Worse still,] rainfall declines of 40-50% [are expected in Africa and] across the north of Latin America, including the Amazon.
Run-off will decline by more than precipitation because of higher rates of evaporation before the water reaches streams and rivers.
[As a result] around 1 billion people … will be exposed to increased water-resource stress.
[Around] 15% of land currently suitable for cultivation will become unsuitable, while in cold regions the area suitable for cultivation increases by 20%. …
[The] poor and vulnerable will be hardest hit by climate change, even though they are not responsible for causing it and [are least able] to defend themselves against it.
[In] sub-Saharan Africa … rain-fed agriculture in many areas would cease to be viable by the end of the century [displacing about 200 million people.]
(pp 195-201)
[Once] the dramatic implications of the climate crisis are recognised by the powerful as a threat to themselves and their children they will, unless resisted, impose their own solutions on the rest of us, ones that will protect their interests and exacerbate unequal access to the means of survival, leaving the weak to fend for themselves.
This is how it has always been. …
Reclaiming democracy for the citizenry is the only way to … ensure that the wealthy and powerful cannot protect their own interests at the expense of the rest.
(pp 223-224)
(Requiem for a Species, 2005)
Contents
Foreword
Executive Summary
Introduction
Observations and Impacts
21st Century Projections
Sectoral Impacts
Would you like to know more?
World Bank
- Turn Down the Heat: Why a 4 degree centigrade warmer world must be avoided, Potsdam Institute for Climate Impact Research and Climate Analytics, International Bank for Reconstruction and Development / The World Bank, November, 2012.
Foreword
The lack of action on climate change not only risks putting prosperity out of reach of millions of people in the developing world, it threatens to roll back decades of sustainable development.
(p ix)
Our work on inclusive green growth has shown that — through more efficiency and smarter use of energy and natural resources — many opportunities exist to drastically reduce the climate impact of development, without slowing down poverty alleviation and economic growth.
(p ix)
Executive Summary
Even with the current mitigation commitments and pledges fully implemented, there is roughly a 20% likelihood of exceeding 4°C by 2100.
If they are not met, a warming of 4°C could occur as early as the 2060s. …
… Small Island Developing states (SIDS) and Least Developed Countries (LDCs) have identified global warming of 1.5°C as warming above which there would be serious threats to their own development and, in some cases, survival …
[The] sum total of current policies … will very likely lead to warming far in excess of these levels. …
Uncertainties remain in projecting the extent of both climate change and its impacts.
We take a risk-based approach in which risk is defined as impact multiplied by probability: an event with low probability can still pose a high risk if it implies serious consequences.
No nation will be immune to the impacts of climate change.
However, the distribution of impacts is likely to be … tilted against many of the world’s poorest regions which have the least … capacity to cope and adapt. …- [Although] absolute warming will be largest in high latitudes, the warming that will occur in the tropics is larger when compared to the historical range of temperature and extremes to which human and natural ecosystems have adapted and coped.
[Unprecedented] high-temperature extremes in the tropics will consequently lead to significantly larger impacts on agriculture and ecosystems. - Sea-level rise is likely to be 15 to 20% larger in the tropics than the global mean.
- Increases in tropical cyclone intensity are likely to be felt disproportionately in low-latitude regions.
- Increasing aridity and drought are likely to increase substantially in many developing country regions located in tropical and subtropical areas.
[Numerous] studies show that there are technically and economically feasible emissions pathways to hold warming likely below 2°C.
Observed Impacts and Changes to the Climate System
[Since 2007,]- The concentration of … carbon dioxide (CO2), has continued to increase from its preindustrial concentration of approximately 278 parts per million (ppm) to over 391 ppm in September 2012, with the rate of rise now at 1.8 ppm per year.
- The present CO2 concentration is higher than … at any time in the last 15 million years.
- Emissions of CO2 are [currently] about 35,000 million metric tons per year [and] are projected to rise to 41,000 million metric tons of CO2 per year in 2020.
- Global mean temperature has continued to increase and is now about 0.8°C above preindustrial levels. …
[A] global mean temperature increase of 4°C approaches the difference between temperatures today and those of the last ice age, when much of central Europe and the northern United States were covered with kilometers of ice and global mean temperatures were about 4.5°C to 7°C lower.
And this magnitude of [human induced] climate change … is occurring over a century, not millennia.
[About] 90% of the excess heat energy trapped by the increased greenhouse gas concentrations since 1955 [has been buffered by] the oceans.
The average increase in sea levels around the world over the 20th century has been about 15 to 20 centimeters.
Over the last decade the average rate of sea-level rise has increased to about 3.2 cm per decade.
[At this rate there will be] over 30 cm of additional sea-level rise in the 21st century.
[Accelerating] loss of ice from the Greenland and Antarctic ice sheets … could add substantially to sea-level rise in the future.
Overall, the rate of loss of ice has more than tripled since the 1993–2003 period as reported in the IPCC AR4, reaching 1.3 cm per decade over 2004–08 …
[The] 2009 loss rate is equivalent to about 1.7 cm per decade.
[Without further] acceleration, the increase in global average sea level due to this source would be about 15 cm by the end of the 21st century. …
[Arctic sea ice] reached a record minimum in September 2012, halving the area of ice covering the Arctic Ocean in summers over the last 30 years. …
The last decade has seen an exceptional number of extreme heat waves around the world …
Preliminary estimates for the 2010 heat wave in Russia put the death toll at 55,000, annual crop failure at about 25%, burned areas at more than 1 million hectares, and economic losses at about US$15 billion (1% gross domestic product). …
Observations indicate a tenfold increase in the surface area of the planet experiencing extreme heat since the 1950s.
The area … affected by drought has also likely increased substantially over the last 50 years, somewhat faster than projected by climate models.
The 2012 drought in the United States impacted about 80% of agricultural land, making it the most severe drought since the 1950s.
[Since] the 1980s global maize and wheat production may have been reduced significantly [due to higher temperatures.]
(p xiv)
[Higher] temperatures substantially reduce economic growth [including agricultural and] industrial output, and political stability [in poor countries.]
Projected Climate Change Impacts in a 4°C World
The largest warming will occur over land and range from 4°C to 10°C.
Increases of 6°C or more in average monthly summer temperatures would be expected in large regions of the world, including the Mediterranean, North Africa, the Middle East, and the contiguous United States Projections for a 4°C world show a dramatic increase in the intensity and frequency of high-temperature extremes. …
[The] coolest months are likely to be substantially warmer than the warmest months at the end of the 20th century.
In regions such as the Mediterranean, North Africa, the Middle East, and the Tibetan plateau, almost all summer months are likely to be warmer than the most extreme heat waves presently experienced.
For example, the warmest July in the Mediterranean region could be 9°C warmer than today’s warmest July. …
Extreme heat waves in recent years have had severe impacts [including] heat-related deaths, forest fires, and harvest losses.
The impacts of the extreme heat waves projected for a 4°C world … could be expected to vastly exceed the consequences experienced to date …
Rising CO2 Concentration and Ocean Acidification
A warming of 4°C or more by 2100 would correspond to a CO2 concentration above 800 ppm and an increase of about 150% in acidity of the ocean.
The observed and projected rates of change in ocean acidity over the next century [are] unparalleled in Earth’s history.
Evidence is already emerging of the adverse consequences of acidification for marine organisms and ecosystems, combined with the effects of warming, overfishing, and habitat destruction.
Coral reefs … are acutely sensitive to changes in water temperatures, ocean pH, and … tropical cyclones.
Reefs provide protection against coastal floods, storm surges, and wave damage as well as nursery grounds and habitat for many fish species.
Coral reef growth may stop as CO2 concentration approaches 450 ppm [—] corresponding to a warming of about 1.4°C in the 2030s …
By the time the concentration reaches around 550 ppm (corresponding to a warming of about 2.4°C in the 2060s), it is likely that coral reefs in many areas would start to dissolve.
The regional extinction of entire coral reef ecosystems … could occur well before 4°C is reached …
Rising Sea Levels, Coastal Inundation and Loss
[Even] if global warming is limited to 2°C, global mean sea level could continue to rise, with some estimates ranging between 1.5 and 4 meters above present-day levels by the year 2300.
Sea-level rise would likely be limited to below 2 meters only if warming were kept to well below 1.5°C.
Sea-level rise … is projected to be up to 20% higher in the tropics and below average at higher latitudes.
[Melting] of the ice sheets will [reduces] the gravitational pull on the ocean toward the ice sheets and [consequently,] ocean water will tend to gravitate toward the Equator.
(p xv)
Of the impacts projected for 31 developing countries … 10 cities account for two-thirds of the total exposure to extreme floods.
Highly vulnerable cities are to be found in Mozambique, Madagascar, Mexico, Venezuela, India, Bangladesh, Indonesia, the Philippines, and Vietnam.
Risks to Human Support Systems: Food, Water, Ecosystems, and Human Health
[Most] adverse impacts on water availability are likely to occur in association with growing water demand as the world population increases. …- Drier conditions are projected for southern Europe, Africa (except some areas in the northeast), large parts of North America and South America, and southern Australia …
- Wetter conditions are projected in particular for the northern high latitudes — that is, northern North America, northern Europe, and Siberia — and in some monsoon regions.
Some regions may experience reduced water stress … - Subseasonal and subregional changes to the hydrological cycle are associated with severe risks, such as flooding and drought, which may increase significantly even if annual averages change little. …
[Extremes] of rainfall and drought projected to increase with warming …
In a 2°C world [mean] annual runoff is projected to- decrease by 20 to 40% in the Danube, Mississippi, Amazon, and Murray Darling river basins, but
- increase by roughly 20% in both the Nile and the Ganges basins.
In Amazonia, forest fires could as much as double by 2050 with warming of approximately 1.5°C to 2°C above preindustrial levels.
Changes would be expected to be even more severe in a 4°C world. …
The IPCC AR4 projected that global food production would increase … in the range of 1°C to 3°C, but may decrease beyond these temperatures.
[However, more recent research suggests] rapidly rising risk of crop yield reductions as the world warms.
Large negative effects have been observed at high and extreme temperatures in several regions including India, Africa, the United States, and Australia.
For example, significant nonlinear effects have been observed in the United States for local daily temperatures increasing to 29°C for corn and 30°C for soybeans.
(p xvi)
[Mid-latitude] coastal areas [are likely to be impacted by increased] seawater penetration into coastal aquifers used for irrigation of coastal plains.
Further risks are posed by … increased drought in mid-latitude regions and increased flooding at higher latitudes. …
[Major] floods that interfere with food production, could also induce nutritional deficits and [increase the] incidence of epidemic diseases [by compromising water supplies.]
[Substantial] increases in [childhood] stunting due to malnutrition are projected to occur with warming of 2°C to 2.5°C, especially in Sub-Saharan Africa and South Asia, and this is likely to get worse at 4°C. …
[Furthermore, changes] in temperature, precipitation rates, and humidity influence vector-borne diseases (for example, malaria and dengue fever) as well as hantaviruses, leishmaniasis, Lyme disease, and schistosomiasis.
Risks of Disruptions and Displacements in a 4°C World
The projected impacts on water availability, ecosystems, agriculture, and human health could lead to large-scale displacement of populations and have adverse consequences for human security and economic and trade systems. …
As global warming approaches and exceeds 2°C, the risk of … abrupt climate change impacts and unprecedented high-temperature climate regimes, increases. …- the disintegration of the West Antarctic ice sheet leading to more rapid sea-level rise …
- large-scale Amazon dieback … potentially adding substantially to 21st-century global warming. …
[Most] of our current crop models do not … fully account for [nonlinear temperature effects, or for] the potential increased ranges of variability [in yields and/or quality of grains due to]- extreme temperatures,
- new invading pests and diseases [or]
- abrupt shifts in critical climate factors …
Projections of damage costs … do not provide an adequate consideration of cascade effects (for example, value-added chains and supply networks) at national and regional scales.
(p xvii)
As the scale and number of impacts grow with … interactions between them might increasingly occur [—] compounding [the] overall impact.
(p xviii)
Introduction
Improvements in knowledge have reinforced the findings of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), especially with respect to an increasing risk of rapid, abrupt, and irreversible change with high levels of warming.
These risks include, but are not limited, to …- Meter-scale sea-level rise by 2100 caused by the rapid loss of ice from Greenland and the West Antarctic Ice Sheet
- Increasing aridity, drought, and extreme temperatures in many regions, including Africa, southern Europe and the Middle East, most of the Americas, Australia, and Southeast Asia
- Rapid ocean acidification with wide-ranging, adverse implications for marine species and entire ecosystems
- Increasing threat to large-scale ecosystems, such as coral reefs and a large part of the Amazon rain forest
Various climatic extremes can be expected to change in intensity or frequency, including heat waves, intense rainfall events and related floods, and tropical cyclone intensity. …
A new generation of studies is indicating adverse impacts of observed warming on crop production regionally and globally …
[These] results indicate a greater sensitivity to warming [and] larger risks for global and regional food production than in earlier assessments. …
There is also a growing literature on the potential for cascades of impacts …
The increasing fragility of natural and managed ecosystems and their services is … expected to diminish the resilience of global socioeconomic systems, leaving them more vulnerable to nonclimatic stressors and shocks, such as emerging pandemics, trade disruptions, or financial market shocks.
(p 1)
The impacts of these changes are likely to be severe and to undermine sustainable development prospects in many regions. …
This report … is focused on developing countries while recognizing that developed countries are also … at serious risk of major damages from climate change.- Chapter 2 summarizes some of the observed changes to the Earth’s climate system and their impacts on human society that are already being observed.
- Chapter 3 provides some background on the climate scenarios referred to in this report and discusses the likelihood of a 4°C warming.
It also examines projections for the coming century on- the process of ocean acidification,
- changes in precipitation that may lead to droughts or floods, and
- changes in the incidence of extreme tropical cyclones.
- Chapters 4 and 5 provide an analysis of projected sea-level rise and increases in heat extremes …
- Chapter 6 discusses the implications [for] agriculture, water resources, ecosystems, and human health.
- Chapter 7 provides an outlook on the potential risks of nonlinear impacts and identifies where scientists’ understanding of a 4°C world is still very limited. …
[The] distribution of impacts is likely to be inherently unequal and tilted against many of the world’s poorest regions …
[These regions also] have the least economic, institutional, scientific, and technical capacity to cope and adapt …
[This combination of] low adaptive capacity [and] disproportionate burden of impacts places them among the most vulnerable parts of the world. …
This report is … intended to provide development practitioners with a brief sketch of the challenges a warming of 4°C above preindustrial levels …
[Further] mitigation action as the best insurance against an uncertain future.
(p 2) - [Although] absolute warming will be largest in high latitudes, the warming that will occur in the tropics is larger when compared to the historical range of temperature and extremes to which human and natural ecosystems have adapted and coped.
