Turn Down The Heat - Why a 4°C warmer world must be avoided.

Turn Down The Heat

In November 2012, The World Bank, an organisation whose motto is "Working for a world free of poverty", launched "Turn Down The Heat - Why a 4°C Warmer World Must be Avoided.". The "Turn Down the Heat" report explores and exposes the severe consequences of allowing climate change to heat the planet by 4 degrees centigrade, especially for those people living in developing countries.

This articles presents a summary of the "Turn Down the Heat" report. We also highlight actions that we can all take to make a 4°C warmer world less likely (see LHS sidebar).

Observed Impacts and Changes to the Climate System

The "Turn Down the Heat" report starts with acknowledging that the scientific consensus on Climate Change is a given, stating

"The science is unequivocal that humans are the cause of global warming, and major changes are already being observed: global mean warming is 0.8°C above pre industrial levels; oceans have warmed by 0.09°C since the 1950s and are acidi- fying; sea levels rose by about 20 cm since pre-industrial times and are now rising at 3.2 cm per decade; an exceptional number of extreme heat waves occurred in the last decade; major food crop growing areas are increasingly affected by drought.".

The report expands on the current research of the Fourth Assessment report (AR4) of the Intergovernmental panel on Climate Change (IPCC) to conclude that every further year of inaction on curbing our Greenhouse gas emissions increases the likelyhood of the planet warming by 4°C by 2100.

Atmospheric CO2 levels

The chapter outlines the current data and trends of observed impacts and changes to the Climate sysem as a result of climate chage to date. Highlighting the current data on rising sea levels, global temperature, heat waves, drought and aridity, as well as the impact on agriculture and the increased frequency of extreme weather events.

However, it is the concluding table of record-breaking meteorlogical events since 200, their societal impacts and qualitative confidence level that the event can be attributed to climate change, that best highlights the challenges we'd face should we allow the planet to heat by 4°C by 2100.

The following extreme weather examples are seen (with high confidence) to be the result of climate change:

  • Europe (2003) - Hottest summer in at least 500 years - Death toll exceeding 70,000
  • Eastern Mediteranean, Middle-EAst (2008) - Driest winter since 1902 - Substantial damage to cereal production
  • 4 US States(TX, OK, NM, LA) (2011) - Record breaking summer heat and drought since 1880 - Wildfires burning 3 million acres(preliminary impact $6 to $8 billion)

21st Century Projections

The third chapter of the report looks at "21st Century Projections" based on the scenarios (SRES - Special report on Emissions Scenarios) developed and used by the Fourth Assessment report (AR4) of the Intergovernmental panel on Climate Change (IPCC).

The report states: "The emission pledges made at the climate conventions in Copenhagen and Cancun, if fully met, place the world on a trajectory for a global mean warming of well over 3°C. Even if these pledges are fully implemented there is still about a 20 percent chance of exceeding 4°C in 2100.10 If these pledges are not met then there is a much higher likelihood—more than 40 percent—of warming exceeding 4°C by 2100, and a 10 percent possibility of this occurring already by the 2070s, assuming emissions follow the medium business-as-usual reference pathway." (Turn Down The Heat, page 23).

CO2 Concentration and Ocean Acidification - impact of coral reefs

Increased CO2 emissions are modelled to increase ocean acidification (as increased CO2 levels dissolve in the ocean), these increasing levels are predicted in to cause coral reefs to stop growing by 2025, and start dissolving by 2050.

Droughts and Precipitation

Climate modelling, observations and theoretical considerations suggest that increased greenhouse-gas levels lead to an intensification of the water cycle. This would result in dry areas becoming dryer and wet areas wetter. For wet area an increase in precipitation of 20-30 % is predicted, with a increase of extreme precipitation events also becoming more common. Dry areas will experience less precipitation and periods of extreme drought, increasing the challenge in poor countries of growing sufficient food for their populations.

Tropical Cyclones

For some coastal areas the projected increased intensity of tropical cyclones poses substantial risks, with these areas likely to experience tropical cyclones of increased intensity (defined by maximum speed). The report states "that warming reaching roughly 4°C by 2100 is likely to double the present economic damage resulting from the increased projected frequency of high-intensity tropical cyclones accompanying global warming, with most damages concentrated in North America, East Asia, and the Caribbean and Central American region." (Turn Down The Heat, page 27)..

Sea-level Rise Projections

Predicting future sea-level rises as a result of global warming of 4°C is achieved through combining thermal expansion of water (as it heats up) with projected melt in mountain glaciers and ice caps (i.e. Greenland and Antarctic ice sheets). The unprecedented rate at which the globe is warming means that we have no historical precedent upon which to base predictions. While a steady state increase in sea-levels estimates a sea level rise of 50 cm and 1m above 2000 sea-level by 2100, several specific warming events, such as a possible collapse of the West Antarctic Ice Sheet, have been identified to have the potential to further raise the global sea level by an additional 3.3 metres.

Much of the rise in sea levels would be concentrated along the equator (due to the spin of the Earth) and would most effect coastal cities and Islands in these areas.

Changes in Extreme Temperatures

The report states " is very likely that the length, frequency, and intensity of heat waves will increase over most land areas, with more warming resulting in more extremes." (Turn Down The Heat, page 37)..

However, it is in the detail of this statement that the direness of the predictions become clear."Temperature anomalies that are associated with highly unusual heat extremes today (namely, 3-sigma events occurring only once in several hundreds of years in a stationary climate)12 will have become the norm over most (greater than 50 percent) continental areas by the end of the 21st century. Five-sigma events, which are now essentially absent, will become common, especially in the tropics and in the Northern Hemisphere (NH) mid-latitudes during summertime.".

An example of a 3-sigma event is the abnormally hot European summer of 2003 (which resulted in 70,000 deaths). This level of summer heat is predicted to occur every second summer by 2100 in a 4°C hotter world. In addition, even more extreme heat events ("five-sigma") will also occur.

The extreme heat waves predicted in the 4°C hotter world would pose enormous adaptation challenges for societies, with high heat mortality increasing. IN additaion agriculture and ecosystems would be strongly impacted and result in severe yeild loss. In poorer countries this would likely lead to famine.

Sectoral Impacts

The World Bank report is focuses on what impact a a 4°C hotter world would have on people living in developing countries, i.e. those people with the least resources, and tragically those people that have contributed least to the onset of climate change.


Food needs over the period to 2100 will increase with the predicted increase in population (which is anticipated to peak in 2050) and climate change impacts our ability to produce this food in three ways. These are:

  1. Temperature - induced effects - increased temperatures may increase yields at higher latitudes (i.e. Siberia), however crops at lower latitudes (i.e. Egypt) will have lower yields. Extreme heat events will further limit agriculture.
  2. Precipitation - induced effects - Drough will increase in likelhood and areas affected by 2100 with "The total “drought disaster- affected” area is predicted to increase from currently 15.4 percent of global cropland to 44 ±6 percent by 2100 based on a modified Palmer Drought Severity Index." (Turn Down The Heat, page 45).
  3. Uncertainty in CO2-fertilisation effect - The current research is unable to provide certainty about the potentially positive impact of increased levels of CO2 on plant growth.

The availability of water for food production looms as the critical factors when it comes to direct impacts on humans. The availability and reliability of water required to produce a certain amount and type of food in a given location. In a changing climate the security of this precious resource cannot be assumed. With decreased precipitation predicted, there will be decreasing water availability in many regions across the tropics and subtropics, including large parts of Africa, the Mediterranean, the Middle East, and parts of Asia, it is these region's whose food production will be most at risk by 2100.

In addition, a portion of the worlds food is grown in coastal lowlands and river deltas. These areas will be increasingly susceptible to sea level rises and extreme precipitation events (i.e. floods). As a result, societies with agriculture in coastal areas and river flood plains face an additional threat to their food supply.

Ecosystems and Biodiversity

The "Turn Down The Heat" report states that a 4°C world is likely to have the following implications for ecosystems and biodiversity:

  • If greenhouse gas emissions and other stresses continue at or above current rates, the resilience of many ecosystems is likely to be exceeded by an unprecedented combination of change in climate, associated disturbances (for example, flooding, drought, wildfire, insects, and ocean acidification) and other stressors (global change drivers) including land use change, pollution and over-exploitation of resources.
  • Approximately 20 to 30 percent of plant and animal species assessed so far are likely to be at increased risk of extinction, if increases in global average temperature exceed of 2–3° above preindustrial levels.

"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. Such damages to ecosystems would be expected to dramatically reduce the provision of ecosystem services on which society depends (e.g., hydrology—quantity flow rates, quality; fisheries (corals), protection of coastline (loss of mangroves)." (Turn Down The Heat, page 49).

Human Health

In a 4°C warmer world the following health issues are anticipated to be exacerbated for all people. However, the impact of these climate change based health issues bwill be most heavily borne by people in developing countries. The adverse effects of warming on human health are:

  • Undernourishment and Malnourishment - "... malnutrition and under-nutrition, which are major contributors to child mortality in developing countries, are likely to increase as an effect of potential crop failure resulting from extreme weather events and changing climate patterns." (Turn Down The Heat, page 54).
  • Health impact of Extreme Events - The impact of flooding, heat waves and other extreme weather events resulting from a 4°C warming is hard to project as adaptive measure can be taken to ameliorate these impacts if societies are able. However, examples such as the European heat wave in 2003 (70,000 deaths) used to indicate the potential damage resulting from extreme weather becoming more common (and further extreme levels emerging). Once again the impact of extreme weather will fall most heavily on those societies least able to adapt, prepare and recover from these events.
  • Mental health and lifestyle-related health discorders - With decreased security of food, water and safety from extreme weather it is anticipated that mental and societal health will decline. "It can be expected that warmer temperatures and exposure to extreme weather events will have negative effects on psychological and mental health as well as increase the occurrence of conflict and violence." (Turn Down The Heat, page 55).. However, research into this area is limited.
  • The spread of pathogens and vector borne diseases - The report states that "Changes in temperature, precipitation and humidity influence vector-borne diseases (for example, malaria and dengue fever), as well as hantaviruses, leishmaniasis, Lyme disease and schis- tosomiasis (World Health Organization, 2009)." (Turn Down The Heat, page 55). It then estimates that for malaria,"The total population at risk in 2050 is projected to be about 5.2 billion if only climate impacts are considered..."
  • Further factors of vulnerability - The report then identifies that "Vulnerability toward health impacts of temperature extremes varies from different subgroups of population. Mid and low income countries face more challenges compared to OECD countries. Children and women are generally expected to be affected more severely (WHO, 2009; (EACC Synthesis World Bank Group, 2010))." (Turn Down The Heat, page 56).
    The report also identifies that indigenous populations (decline of local wildlife and traditional food), island residents (rising sea levels) and city dwellers (heat trapped in cities) are all exposed to additional health issues arising from a 4°C warmer world.

System Interaction and Non-Linearity

"Although systems interact, sometimes strongly, present tools for projecting impacts of climate change are not yet equipped to take into account strong interactions associated with the intercon- nected systems impacted by climate change and other planetary stresses, such as habitat fragmentation, pollution, and invasive species (Warren 2011). Scientific findings are starting to indicate that some of these interactions could be quite profound, rather than second-order effects. Impacts projected for ecosystems, agri- culture, and water supply in the 21st century could lead to large- scale displacement of populations, with manifold consequences for human security, health, and economic and trade systems. Little is understood regarding the full human and economic consequences of a collapse of coral reef ecosystems, combined with the likely concomitant loss of marine production because of rising ocean temperatures and increasing acidification, and the large-scale impacts on human settlements and infrastructure in low-lying fringe coastal zones of a 1 m sea-level rise within this century. While each of these sectors have been examined, as yet researchers do not fully understand the consequences for society of such wide ranging and concomitant impacts, many of which are likely before or close to 4°C warming." (Turn Down The Heat, page 59).

Risks of nonlinear and Cascading impacts

"With global warming exceeding 2°C, the risk of crossing activa- tion thresholds for nonlinear tipping elements in the Earth System and irreversible climate change impacts increases (Lenton et al. 2008), as does the likelihood of transitions to unprecedented climate regimes. " (Turn Down The Heat, page 60).

the following are examples of identified nonlinear events that would greatly incease the risks for humanity:

  • Amazon Rain Forest Die-back - "There is a significant risk that the rain forest covering large areas of the Amazon basin will be lost as a result of an abrupt transition in climate toward much drier conditions and a related change in the vegetation system." (Turn Down The Heat, page 60).
  • Ocean Ecosystems - "The rising atmospheric carbon dioxide concentration is leading to rapid acidification of the global ocean. Higher acidity (namely, lower pH) of ocean waters leads to reduced availability of calcium carbonate (ara- gonite), the resource vital for coral species and ecosystems to build skeletons and shells." (Turn Down The Heat, page 61).
  • West Antarctic Ice Sheet - "It has long been hypothesized that the West Antarctic Ice Sheet, which contains approximately 3 m of sea-level rise equivalent in ice, is especially vulnerable to global warming (Mercer 1968; 1978)." (Turn Down The Heat, page 61).
  • Greenland Ice Sheet - "New estimates for crossing a threshold for irreversible decay of the Greenland ice sheet (which holds ice equivalent to 6 to 7 m of sea level) indicate this could occur when the global average temperature increase exceed roughly 1.5°C above preindustrial (range of 0.8 to 3.2°C) (Robinson et al. 2012)." (Turn Down The Heat, page 61).

Concluding remarks

"A 4°C world will pose unprecedented challenges to humanity. It is clear that large regional as well as global scale damages and risks are very likely to occur well before this level of warming is reached." (Turn Down The Heat, page 64).

"Given that it remains uncertain whether adaptation and further progress toward devel- opment goals will be possible at this level of climate change, the projected 4°C warming simply must not be allowed to occur—the heat must be turned down. Only early, cooperative, international actions can make that happen." (Turn Down The Heat, page 64).


Leave a Comment

You must be signed in to leave a comment. Log in.