Introduction

The IPCC (Intergovernmental Panel on Climate Change) consists of three working groups who publish reports every 6 years describing the current understanding of all aspects of climate change (CC). The previous blog post (Key Figures from the IPCC’s AR5 Report) gives an introduction into the IPCC and explains the key figures published by the First Working Group last winter which concentrates on the scientific evidence of CC. This blog post summarises the highlights from the Second Working Group (WG2) which aimed to assess the risks associated with CC, particularly Impacts, Adaptation and Vulnerability.

WG2’s Summary for Policy Makers, which this post is based upon, assesses relevant scientific, technical and socioeconomic literature. Such literature is comprised of empirical observations, experimental results, process-based understanding, statistical approaches, simulation and descriptive models as well as expert judgement.

NB: For descriptions of the confidence and certainty values mentioned in this post please see this previous post on the WG1 report.

Current Observed Impacts, Vulnerability, and Exposure

The figure below summarises the observed impacts around the world in the last few decades. A hollow symbol means that the evidence suggests CC has had a minor impact, and a filled symbol represents a major CC contribution. The rectangular bars beside each symbol represent the confidence associated with each impact. A summary of the major themes found throughout the impacts stated on this map are listed below. All statements are stated to have high or medium confidence levels.

• Changes in precipitation or melting snow / ice is altering some regions’ hydrological systems, which can affect water resources and quality.
• Many species have shifted their geographic ranges, seasonal migration times, abundances etc. A few species have become extinct due to current CC.
• Negative impacts of CC on crop yields currently outweigh positive impacts. Positive impacts are mainly localised to the Northern hemisphere higher latitude regions.
• Currently, the impact of CC on worldwide human health is minimal when compared with other contributing factors. It should be noted that there has been an increase in heat related mortality and a decrease in cold related mortality.
• Climate extremes, for example, heat waves, droughts, floods (which are expected to increase in the future) are a significant vulnerability for some ecosystems.
• Climate related hazards aggravate other stressors that impact human life, especially for people living in poverty. For example, food price increases due to lower crop yields. Observed positive impacts are limited and often indirect, for example, diversification of agricultural practices.

Widespread impacts in a changing world. (A) Global patterns of impacts in recent decades attributed to climate change, based on studies since the AR4. Impacts are shown at a range of geographic scales. Symbols indicate categories of attributed impacts, the relative contribution of climate change (major or minor) to the observed impact, and confidence in attribution.

The following diagram shows regional examples of the impacts described in the previous paragraph. For a more comprehensive list of impacts please see the Summary for Policy Makers Table 1. All statements listed below have confidence levels shown in brackets after each impact.

The figure below shows the average percentage change in crop yield. The two blue bars to the left show all crops grouped as growing in tropical or temperate climates. The four orange bars on the right are the most common crops worldwide. It has been observed on the whole that CC has had a negative impact on yields of most crops worldwide.

(C) Summary of estimated impacts of observed climate changes on yields over 1960-2013 for four major crops in temperate and tropical regions, with the number of data points analyzed given within parentheses for each category.

Risks in the Future

The second half of the summary for policy makers concentrates on the future risks and possible benefits CC will bring to the world. The magnitude and rate of CC is also taken into consideration. The IPCC Working Group 1 used four representative concentration pathway (RCP) scenarios to predict the average global temperature leading up to 2100. For definitions of the RCP scenarios please read my last post. The following risks predicted by the WG2 all occur in at least one of the RCP scenarios and all possess high confidence levels.

• Risk of death, injury, ill-health, or disrupted livelihoods in low-lying coastal zones and small island developing states and other small islands, due to storm surges, coastal flooding and rising sea level.
• Risk of severe ill-health and disrupted livelihoods for large urban populations due to inland flooding in some regions.
• Systemic risks due to extreme weather events leading to breakdown of infrastructure networks and critical services such as electricity, water supply, and health and emergency services.
• Risk of increases in mortality and disease during periods of extreme heat, particularly of vulnerable urban populations and those working outdoors.
• Risk of food insecurity and the breakdown of food systems linked to warming, drought, flooding, and precipitation variability and extremes, particularly for poorer populations in urban and rural settings.
• Risk of loss of rural livelihoods and income due to insufficient access to drinking and irrigation water and reduced agricultural productivity, particularly for farmers and pastoralists with minimal capital in semi-arid regions.
• Risk of loss of marine and coastal ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for coastal livelihoods, especially for fishing communities in the tropics and Arctic.
• Risk of loss of terrestrial and inland water ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for livelihoods.
• Many key risks constitute particular challenges for the least developed countries and vulnerable communities, given their limited ability to cope.

Future Risks by Sector

• Freshwater resources: Risks increase significantly as concentrations increase (robust evidence, high agreement). Renewable surface- and groundwater resources are expected to decrease over the 21^st century especially in subtropical dry regions which would intensify competition for water supply (limited evidence, medium agreement).
• Terrestrial & freshwater ecosystems: Both ecosystems are expected to have a large fraction facing extinction risks during and beyond the 21^st century. This is because CC can have an impact on other factors such as pollution, invasive species etc. (high confidence). There is also the risk of abrupt and irreversible regional-scale change in the higher RCP scenarios (medium confidence).
• Coastal & low-lying areas: Rising sea levels are predicted throughout the 21^st century. Coastal and low-lying areas will therefore increasingly experience adverse impacts such as flooding and coastal erosion (very high confidence).
• Marine systems: Global marine-species redistribution and marine-biodiversity reduction will challenge the sustained provision of fisheries productivity (high confidence). For medium to high RCPs, ocean acidification will cause substantial risks particularly to coral reefs and polar regions (medium – high confidence).
• Food security & food productions systems:  Major crops will see a negative impact on production without adaptation, however individual locations may benefit (medium confidence). All aspects of food stability are affected by CC, including food access and price stability (high confidence).
• Urban areas: Urban areas are affected by many CC risks (medium confidence). Risks are amplified for those lacking appropriate infrastructure, those in poor quality housing and in exposed areas (medium confidence).
• Rural areas: Rural areas are exposed to both near- and long-term risks from CC. These impacts include water availability, supply and food shortages (high confidence).
• Key economic sectors & services: For economic sectors, other stressors, including population, technology, relative prices etc. will be larger than the impacts of CC (medium confidence). Global economic impacts from CC are very difficult to estimate. The most recent, but still incomplete, estimates predict an increase of ~2 ^oC would have a negative economic effect of between 0.2 and 2 % of income (medium evidence, medium agreement).
• Human health: Until mid-century CC will impact human health by exacerbating current health issues (very high confidence). It is expected to increase throughout the 21^st century in many regions, especially developing countries with low income (high confidence).
• Human security: The displacement of people is expected to change due to CC (medium evidence, high agreement). CC can increase violent conflicts in the form of civil war by amplifying well-documented drivers of these conflicts such as poverty and economic shocks (medium confidence).
• Livelihoods & poverty: Throughout the 21^st century CC is expected to reduce economic growth, make poverty reduction more difficult and further erode food security (medium confidence).

Future Surface Temperature Scenarios

The following diagram shows how the Earth’s temperature has changed in the last ~110 years (Part A). Any area with insufficient data was left white and any statistically insignificant temperature change is shown with hatched lines. The second diagram in the figure below (B) shows two of the RCP scenarios and how the world’s average temperature could increase whilst following these scenarios. The blue is considered the ‘best case’ scenario where countries adopt a very strict reduction of greenhouse gas (GHG) emissions whereas the red is a ‘carry on as normal’ scenario. The third part to this figure (C) shows two plots much the same as in part A but the two RCP scenarios have been used to show how the Earth’s surface temperature can change depending on what mitigation techniques are adopted. The percentage temperature increase is taken from the average of the Earth’s temperature from 1986-2001. The key things to note from this figure is how dramatically different the future climate could be and how uneven the warming across the world is (for example, the Northern Hemisphere warms much more than the Southern Hemisphere).

Observed and projected changes in annual average surface temperature. This
figure informs understanding of climate-related risks in the WGII AR5. It illustrates temperature change observed to date and projected warming under continued high emissions and under ambitious mitigation.

Future Fishing Scenarios

The final figure in this post shows the possible changes to fishing by the middle of this  century. The plot shows the redistribution of the maximum catch potential for over 1000 fish species caught worldwide, and is compared to the 2001-2010 baseline value. The values calculated here are based upon one of the more extreme RCP scenarios. Coastal regions and seas in north-western Europe and other mid- to high-northern latitudes will see an increase in maximum catch potential as more warm-water species migrate northwards. There will be a sharp decrease in maximum catch in the equatorial regions and around the South Pole with differences being as small as half the expected value of the 2001-2010 mean.

Climate change risks for fisheries. (A) Projected global redistribution of maximum catch potential of ~1000 exploited fish and invertebrate species. Projections compare the 10-year averages 2001-2010 and 2051-2060 using SRES A1B, without analysis of potential impacts of overfishing or ocean acidification.

 The IPCC WG2 also goes into detail about adaptation strategies however these have not been covered in this blog post. For more detail on this I suggest Section C of the Summary for Policy Makers. The third and final report by the Working Group 3 (WG3) has been published, and concentrates on potential mitigation choices – the subject of my next post.