What are the impacts of climate change?
The impacts of climate change will disrupt the natural, economic and social systems we depend on. This disruption will impact global food security, damage infrastructure and jobs, and harm human health. These impacts are unevenly distributed around the world, with some countries facing far greater risks than others. However, all countries, communities and companies will feel the effects of climate change.
This section explores the impacts that climate change will have on natural and human systems, both in the UK and across the world. It looks at the way climate change could affect the global economy, and it explains why some of the biggest risks for our society are the most difficult to understand.
Impacts of climate change FAQ
How do rising levels of carbon dioxide affect plants and global crop growth?
Human-caused emissions directly affect plants, as higher CO2 levels generally increase photosynthesis and plant growth. It is almost certainly because of this ‘fertilising’ effect that land ecosystems take up more than a quarter of the CO2 emitted by human activities.
Some crops, especially in temperate regions, are expected to grow faster and have higher yields as a result of such increases in CO2. However, because raised CO2 levels are also the cause of climate change, their impacts on plants are not straightforwardly positive. While crops in temperate regions could benefit from warmer weather during their growing season as a result of global warming, the effect of climate change impacts such as droughts and heat-stress are expected to have net negative impacts on crops in many warmer regions of the world.
Photosynthesis depends directly on the amount of light absorbed by leaves, and higher CO2 levels help plants use the light they absorb more efficiently to convert CO2 into biomass. In addition, it also makes plants use water more efficiently. This improved efficiency increases vegetation cover – which further increases the amount of light plants absorb. These effects are part of the reason for an increase in green vegetation cover that can be seen from space; although intensive human use of land for growing crops, particularly in China and India, is also contributing to this ‘global greening’, and could account for up to a third or more of observed net increase in global vegetation cover.
Scientists have explored the effects of CO2 through experiments on ecosystems, including both forests and food crops. They show that increasing CO2 by a further 150–200 parts per million – up from today’s level of around 410 parts per million – increases the rate of photosynthesis in leaves growing under natural light conditions by around 12% on average,.
However, whether specific plants are able to grow faster as CO2 levels rise also depend on several other factors. Some plants – so-called C4 plants, including many tropical grasses, maize and sugarcane – have a mechanism that concentrates CO2 inside their leaves. This means higher CO2 concentrations will not increase their rates of photosynthesis and their growth. This is why yields for maize are not generally expected to increase – except in dry areas where crops are not artificially supplied with water, and where the increased efficiency in using water (due to raised CO2) will benefit growth. Plants’ ability to grow faster in response to increased CO2 concentrations also depends on whether they can access the extra nutrients they need to grow more.
Non-C4 crops, like wheat, soybean and rice, can grow more in rising CO2 concentrations. In one sense, this phenomenon makes increasing CO2 levels ‘good’ for agriculture. On the other hand, risingCO2 levels are causing climate change, which is likely to have a harmful effect on crop growth, for example through heat-stress, especially in regions that are already warm. Future scenarios for crop yields suggest that we will see a mixed outcome, with higher average agricultural production in some regions, but increased risks of crop damage in other regions, particularly in the developing world.
The effects of raised CO2 concentrations on natural ecosystems are also not straightforwardly ‘good’ or ‘bad’. Rising CO2 levels tend to increase tree cover in grasslands, for example, which is ‘good’ for removing carbon from the air but ‘bad’ for grazing animals, as savannas become less grassy. And as raised CO2 levels makes plant water use more efficient, plant coverage can increase so much that it ends up using as much or even more water than before – which can add to the pressures on fresh water supplies in ecosystems with limited water.
That a higher level of CO2 has some positive effects on plant life does not change the fact that continued climate change will have increasingly harmful effects on many aspects of human activity across the globe, including crop growth and agriculture in warmer regions. The outcomes of policies to limit these impacts will take time to come into effect, which makes action towards net-zero emissions an urgent priority.
 Le Quéré, C. et al. (2018) Global carbon budget 2018. Earth System Science Data 10, 2141–2194
 Liu, B. et al. (2018) Global wheat production with 1.5 and 2.0˚C above pre-industrial warming. Global Change Biology 25, 1428–1444
 Cernusak, LA et al. (2019) Robust response of terrestrial plants to rising CO2. Trends in Plant Science 24, 578–586
 Chen, C., Park, T., Wang, X. et al. (2019). China and India lead in greening of the world through land-use management, Nat Sustain 2, 122–129 doi:10.1038/s41893-019-0220-7
 Ainsworth, E. A. and Long, S.P. (2005). What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2. New Phytologist 165, 351-71
 Broberg, M.C. et al. (2019) Effects of elevated CO2 on wheat yield: non-linear response and relation to site productivity. Agronomy 9, 243
 Leakey, A. D. B. (2006) Photosynthesis, productivity, and yield of maize are not affected by open-air elevation of CO2 concentration in the absence of drought. Plant Physiology 140, 779-790
 Terrer, C. et al. (2016) Mycorrhizal association as a primary control of the CO2 fertilization effect. Science 353, 72-74
 Deryng, D. et al. (2014). Global crop yield response to extreme heat stress under multiple climate change futures. Environmental Research Letters 9, 034011
 Ukkola, A. M. et al. (2015) Reduced streamflow in water-stressed climates consistent with CO2 effects on vegetation. Nature Climate Change 6, 75–78
How does climate change lead to sea level rise, and how will this impact coastal cities?
As the world warms, ice sheets and glaciers on land melt and flow into the ocean. The ocean itself also warms and expands, as it absorbs significant amounts of the heat trapped by the greenhouse gas effect. These changes cause the sea level to rise.
Sea level rise continues to speed up as human-induced global warming increases. Sea levels were rising at a rate of around 8cm per 100 years in the late nineteenth century, 21cm per 100 years in the mid-twentieth century, and now up to around 32cm per 100 years. Future sea level rise depends on how quickly we reduce global greenhouse gas emissions.
However, the time lag between temperature rises and the melting of ice means we are already ‘locked in’ to a certain amount of future sea level rise. In a scenario where emissions are reduced rapidly and the rise in global temperatures stay below 2°C, sea level rise will still reach 29–59 cm in the next hundred years with respect to 1986-2005 levels. This is because the effect of CO2 already in the atmosphere has a time lag; it heats the atmosphere slowly.
If emissions continue as they are, and ice-sheets respond to this in an expected manner, sea levels could rise by up by 1 m by 2100 compared to 1986-2005 levels. This would bring serious risks for coastal regions around the world, including low-lying islands and major cities like Shanghai, Alexandria and Miami. More than half of the world’s largest cities lie along the coast, and just over 1 billion people live in coastal areas within 10 metres of sea level. Adaptation measures can help protect these areas against serious risks of flooding if they go beyond maintaining today’s standards of protection and prepare for rising sea levels.
The largest threat of future sea level rise comes from the possibility that the massive ice sheets in the Antarctic and Greenland could melt. In particular, the West Antarctic ice sheet is thought to be vulnerable to collapse. It rests on a bed more than 2 km below sea level and contains enough ice to raise global sea levels by around 3.5 m. In total, there is enough ice on the planet to raise sea levels by 70 m. It is difficult to predict at what level of warming this kind of dangerous change could occur, however the risk grows as global temperatures increase.
 IPCC. (2019).: Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, H.-O. et al. D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. Weyer (eds.)]. In press.
 IPCC. (2019). Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [Pörtner, H.-O. et al. (eds.)]. In press.
 Pelling, M. and Blackburn, S. (eds) (2013). Megacities and the Coast: Risk, Resilience and Transformation. Routledge: Earthwatch.
 Kulp, S.A., Strauss, B.H. (2019). New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications 10, 4844 IPCC, 2019: Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.- O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, M. Nicolai, A. Okem, J. Petzold, B. Rama, N. Weyer (eds.)]. In press
 Hallegatte, S., Green, C., Nicholls, R.J. and Corfee-Morlot, J., 2013. Future flood losses in major coastal cities. Nature climate change, 3(9), p.802.
How will climate change impact our society?
Climate change impacts our society by disrupting the natural, economic and social systems we depend on. This disruption will affect food supplies, industry supply chains and financial markets, damage infrastructure and cities, and harm human health and global development.
The impacts of climate change are already here. Global sea levels have risen 19cm since the beginning of the twentieth century, increasing the risk of flooding for many coastal cities and communities. Heatwaves and droughts are becoming more common and more intense in many parts of the world, causing harm to human health and more heat-related deaths. Climate change is also affecting food security as rain and heat patterns change. In Southern Europe and some parts of Africa, Asia and South America, crop yields are declining.
In the UK, climate change is making some extreme weather events more frequent and more serious. The winter floods in 2013-14, which cost the economy £450 million in insured losses, occurred due to record rainfall in England and Wales and were made more likely by climate change. The European summer heatwave in 2018, which led to wildfires in parts of the UK, was made around 30 times more likely by climate change. Scientists now expect 12% of UK summers to experience the same levels of heat. Before global warming, the risk was less than 0.5%.
As the planet gets warmer, the impacts of climate change will grow. If emissions are not decreased and global warming reaches 4°C by 2100, sea levels in the UK could increase by around 1 m, which would put 3.3 million people at risk of flooding by 2050. Global food supply would also be less secure as extreme weather events and habitat degradation disrupt supply chains. This could lead to higher food prices and up to 183 million more people in the world facing hunger.
Every bit of warming matters, and vulnerable populations and communities across the world have the greatest difficulty coping with the impacts. Even just half a degree of warming can make the difference between dangerous and manageable effects. By limiting global warming to 1.5°C instead of 2°C, for example, 420 million fewer people would be frequently exposed to extreme heatwaves, and 10 million fewer people would be at risk of flooding from rising sea levels.
These risks and impacts are not evenly distributed, and some regions of the planet will feel the effects of climate change more severely than others depending on their location and ability to adapt. However, because both the climate system and our human societies are globally interconnected, the effects of climate change will impact all countries, companies and communities in some way.
 Church, J.A. et al. (2013). Sea Level Change. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F. et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
 IPCC. (2019). Summary for Policymakers. In: IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems.
 Kendon, M. et al. (2015) State of the UK Climate 2014. Met Office, Exeter, UK.
 Schaller, N. et al. (2016) Human influence on climate in the 2014 southern England winter floods and their impacts. Nature Climate Change, 6, 627–634
 Met Office. (2018) Chance of summer heatwaves now thirty times more likely [Accessed 11th November 2019]
 Lowe, J. et al. (2019) UKCP18 Science Overview Report. Met Office.
 Adaptation Sub-Committee of the Committee on Climate Change. (2016). UK Climate Change Risk Assessment 2017 Synthesis Report: Priorities for the Next Five Years. London, 2016.
 IPCC. (2019). Summary for Policymakers: IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems.
 Hoegh-Guldberg, O., D. et al. (2018). Impacts of 1.5ºC Global Warming on Natural and Human Systems. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. et al (eds.)]. In Press
What are the impacts of climate change on the economy?
The physical impacts of climate change will affect most aspects of human welfare and the economy. In some regions of the world, rising temperatures will harm worker productivity and crop yields, and lead to more cardiovascular and respiratory problems and higher mortality rates; although cold-related mortality rates are likely to fall. Meanwhile, higher sea levels will flood cities, storms will become more damaging, rivers will dry up, glacier-fed water supplies will diminish, and ecosystems will suffer.
Calculations of the costs of these changes are mostly given as a top-level, global average. They are usually given in relation to GDP (‘gross domestic product’) a measure of economic income that is not entirely clear to most of us. GDP is the total economic value of all goods and services produced within a country in a given period; it is used as a standard measure of economic performance.
Some attempts to calculate the total costs of climate change suggest that if the global average temperature increase is kept below 2°C, it will cause economic impacts that are less than 1% of global GDP. In 2017, 1% of global GDP was $800 billion (£648 billion). If temperatures rise further, however, the costs of climate change would increase rapidly. One study suggests unmitigated global warming could reduce average global incomes roughly 23% by 2100, and make 77% of countries poorer in per capita terms than they would be without climate change.
Calculating economic impacts in these average values, however, hides many of the most important issues related to the costs of climate change. Firstly, calculations are hugely uncertain and often do not represent all major risks. Secondly, economic impacts measured in terms of the effects on global GDP look very different at the level of individual countries, and of individual people.
This is because the social and economic impacts of climate change will be distributed unevenly around the world. Some areas will be completely devastated by climate change, such as low-lying islands and coastal towns, and economies that depend a lot on agriculture. These areas are often the poorest parts of the world, where millions are vulnerable to the impacts of climate change, and their economies will be hit the hardest. People living in poverty are the least able to adapt to warming, and small changes in their income due to climate change-related events can result in overwhelming losses to welfare and livelihoods. Calculations at the level of GDP can hide these impacts.
Ultimately, some of the greatest risks are also the ones for which we cannot calculate the costs yet. The climate system has several thresholds and ‘tipping points’, where small differences in temperature can create sudden, unexpected and permanent changes with global consequences. Examples include the collapse of the West Antarctic ice sheet, dieback of the Amazon, failures of the Indian monsoon, and the weakening of Atlantic thermohaline circulation.
Even though these events are individually unlikely, they would have wide-ranging and serious impacts that represent huge economic and social risks. Major changes like these would increase the potential for conflict, political upheaval and mass displacement.
 Carleton, T. A. and Hsiang, S. M. (2016). Social and economic impacts of climate change. Science: Vol. 353, Issue 6304
 Carleton, T. et al. (2018). Valuing the Global Mortality Consequences of Climate Change Accounting for Adaptation Costs and Beneﬁts. Working Paper 2018-51, Becker Friedman Institute for Research In Economics.
 Tol, R.S. (2018). The Economic Impacts of Climate Change, Review of Environmental Economics and Policy, Volume 12, Issue 1, Pages 4–25
 Burke et al. (2015). Global non-linear effect of temperature on economic production. Nature, 527:235–239
 World Bank. (2016). Shock Waves: Managing the Impacts of Climate Change on Poverty. Climate Change and Development Series. Washington, DC: World Bank.
 Lenton TM, et al. (2008) Tipping elements in the Earth’s climate system. Proceedings of the National Academy of Sciences USA 105:1786–1793
 Carleton, T., Hsiang, S. and Burke, M. (2016). Conflict in a changing climate. The European Physical Journal Special Topics, 225: 489
["Faces of the Floods" by Charlie Clift is licensed under CC BY-NC 4.0 ]