Expected effects

Effects on temperature, precipitation, sea level etc.

Photo: Caumasee CC-

In the fifth assessment report IPCC uses four so-called “representative concentration pathways” (RCPs). They are and can briefly be described as follows:

RCP8.5 – continued high emissions of carbon dioxide
RCP6.0 – carbon dioxide emissions peak in 2060
RCP4.5 – carbon dioxide emissions peak in 2040
RCP2.6 – carbon dioxide emissions peak in 2020

The RCP2.6 scenario is the only one where staying below a 2°C temperature increase since preindustrial times is considered as “likely” (66–100% probability).

	Increase in global mean surface temperatures for 2046–2065 relative to 1986–2005, projected as likely.	Increase in global mean surface temperatures for 2081–2100 relative to 1986–2005, projected as likely.
RCP2.6	1.0 (0.4 to 1.6)	1.0 (0.3 to 1.7)
RCP4.5	1.4 (0.9 to 2.0)	1.8 (1.1 to 2.6)
RCP6	1.3 (0.8 to 1.8)	2.2 (1.4 to 3.1)
RCP8.5	2.0 (1.4 to 2.6)	3.7 (2.6 to 4.8)

Warming will continue beyond 2100 under all RCP scenarios except RCP2.6.

Temperatures are not expected to increase evenly around the world. Over the Arctic and land masses in the northern hemisphere, warming will be significantly greater.

Arctic sea ice cover will continue to shrink and thin and the northern hemisphere spring snow cover will decrease as global mean surface temperature rises. Global glacier volume will further decrease. By the end of the 21st century reductions in Arctic sea ice in September range from 43% for RCP2.6 to 94% for RCP8.5.

Near-surface permafrost extent at high northern latitudes will be reduced as global temperature increases. By the end of the 21st century, the area of permafrost near the surface is projected to decrease by between 37% (RCP2.6) to 81% (RCP8.5). This will lead to methane emissions that will further accelerate global warming.

Sea levels will continue to rise. Under all RCP scenarios, the rate of sea level rise is expected to increase compared to the past decades, due to increased ocean warming and increased loss of mass from glaciers and ice sheets.

	Global mean sea level rise 2046–2065 relative to 1986–2005, projected as likely.	Global mean sea level rise 2081–2100 relative to 1986–2005, projected as likely.
RCP8.5	22-38 cm	45-82 cm
RCP6.0	18-32 cm	33-63 cm
RCP4.5	19-33 cm	32-63 cm
RCP2.6	17-32 cm	26-55 cm

Changes in precipitation and drought periods because of global warming are expected to vary between regions. In general, contrasts between wet and dry regions as well as wet and dry seasons are projected to increase, although there may be exceptions. Heavy rainfalls will become more intense and more common over mid-latitude land masses and in wet tropical regions.

Increasing atmospheric carbon dioxide concentrations also lead to increasing acidification of the ocean. Projections give reductions in average global surface ocean pH of between 0.06 and 0.32 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.

Effects on natural world and human society

Photo: Himalayan Trails CC-BY-NC-SA

(Results from IPCC Working Group II)

The IPCC report, published in March 2014, summarizes published scientific research up to 2010. It describes how climate change is affecting people and the environment. It predicts future impacts, by region and sector, and estimates how far mitigation and adaptation measures can help reduce them.

Impacts already here:

Climate change has already led to degraded water resources in many areas due to changes in precipitation and melting of snow and glaciers. Species on land, in fresh waters and in the oceans, have moved to different regions, altered in numbers and changed behaviour to adapt to new climatic conditions. Impacts on crop yields have to a greater extent been negative than positive.

Extreme climate-related events such as heat waves, droughts, floods, cyclones and forest fires have a major impact on both ecosystems and communities.

Inequality in the world is exacerbated by climate change. Already vulnerable people and communities have the greatest difficulties to adapt. Armed conflict increases vulnerability to climate change even further.

What to expect:

Further climate change will have an even greater impact on freshwater resources. The availability of both surface water and groundwater is expected to decrease in most subtropical regions and competition for water will therefore increase.

A large proportion of both land and freshwater species will be at risk of extinction. This is especially true when climate change interacts with other factors that affect habitats, levels of exploitation, pollution and invasive species. Irreversible changes in land and freshwater ecosystems at a regional level are also expected at medium to high emissions scenarios (RCP4.5, 6.0 and 8.5).

The biodiversity of sensitive parts of the sea will decrease, and a redistribution of species in the oceans is also expected. This will change the conditions for sustainable fisheries and other ecosystem services.

Because of sea level rise, coastal and low-lying areas will experience more flooding and increased erosion.

Ocean acidification will at medium to high emissions scenarios (RCP4.5, 6.0 and 8.5) have a significant impact on the marine ecosystem especially for polar ecosystems and coral reefs.

The production of major crops (wheat, rice and maize) in tropical and temperate regions is generally expected to be adversely affected by continued climate change, although there may be regional exceptions.

Impact on human health will initially aggravate already existing health problems. Throughout the 21st century, climate change is expected to lead to increased health problems in many regions, particularly in developing countries with low income, compared to a baseline without climate change.

People will also be compelled to migrate due to altered climate conditions. Climate change may also indirectly increase the risk of violent conflict by enhancing factors that often contribute to conflict, such as poverty and economic crises.

Climate change is expected to slow down economic growth, make poverty reduction more difficult, further worsen conditions for food security, and extend existing poverty traps as well as creating new ones, the latter especially in cities and areas particularly vulnerable to hunger.