Impacts

Sea levels are rising ▼

The rise in sea level is in part due to the higher temperatures melting ice sheets and glaciers, which drain into the oceans. It is also due to the ocean warming: as it warms the ocean expands and so the level of the sea rises. Worldwide the sea level is rising by around 3.3mm a year. It has risen by about 178mm (7 inches) since the beginning of the 20th century, and the rate at which it is rising has nearly doubled.^wmo

• When combined with extreme winds, waves and rainfall, even a small rise in sea level increases hazards for coastal communities, and exposes low-lying islands to a greater risk of flooding (see extreme weather below). With continual melting of ice and expansion from heat, the sea will continue to rise. If the rise in global temperature is limited to 1.5°C, it is estimated that, by 2100, sea level will have risen by about half a metre (0.26-0.77m), relative to the period 1986-2005. This could affect about 600 million people living in low-lying coastal regions and small islands.^wmo Many more people would be at risk if the temperature rose above 1.5°C.

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Arctic sea ice is shrinking ▼

Sea ice expands and thickens in the cooler months of winter, and shrinks and thins in the summer. This means that each year we get a maximum and a minimum expanse of sea ice. With the global rise in temperature, over the last four decades the extent of sea ice has decreased for every month of the year, but particularly when at its minimum extent in summer. The sea ice is also becoming thinner. But why does it matter?

• Loss of ice also causes further warming. When the ice melts, it exposes more of the ocean surface. The ocean is darker than the ice, so it reflects less solar energy (absorbing it instead), which increases the temperature even more.ⁱ This causes more ice to melt, more dark surface to be exposed, more energy to be absorbed by the ocean, more warming and so on. These effects are a key factor in the Arctic warming at a rate 2-3 times the global average.
• Changes in sea ice affect the habitat of many organisms, such as phytoplankton, polar bears, seabirds, walruses and seals. They can adapt to change but it can be dangerous for the young. For example, with less ice, or thinner ice, polar bears are forced to swim more and to travel longer distances for food, but the young bear cubs may not survive the long swim. Similarly young seals can become stranded and die in years when there is not much ice.

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Land ice is shrinking ▼

With higher temperatures, glaciers and the Greenland ice sheet have been shrinking over the last 40 years.^wmo An ice sheet is a large version of a glacier. Both are formed from snow that has fallen over thousands of years and compressed into thick ice masses, and both move like a river, but slowly. The earth has two ice sheets: one covers most of Greenland, and the other covers Antarctica. Glaciers occur across the world, particularly in polar regions and mountainous areas.

The shrinking of ice sheets is expected to accelerate over the coming decades. It is also estimated that we will lose 36% of ice from glaciers if we allow warming to reach 2°C, which is double the estimated loss at 1.5°C. Some of the effects of losing land ice are identified below:

• Melting ice flows into the sea and contributes to sea level rise (see above).
• Glaciers provide freshwater to millions of people through runoff of water from the melting ice, mostly during warmer months. The water feeds into downstream river basins that cover vast areas of land. In the mountainous regions in Asia, for example, the glaciers provide water to 1.4 billion people through several river basins, such as the Indus and Ganges. However, with the shrinking glaciers, the meltwater runoff at some point starts to decline.ⁱ This can threaten the water supply to millions living in areas where the rainfall is low in summer. In the Indus basin alone 120 million people could be affected.^a.g. This has already contributed to declines in agricultural yields in some high mountainous areas, such as parts of the Andes and the Himalayas. In the coming decades the decline in runoff is expected to have further impacts on irrigation and energy production (hydropower).

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Arctic permafrost is thawing ▼

Permafrost is ground that is continuously frozen, and much of it has been frozen for thousands of years. The ground contains soil, rock, sand, vegetation and ice. It covers about a quarter of the land in the northern hemisphere, including regions in Alaska, Siberia and Greenland. It is estimated that it contains about twice the carbon that is in the atmosphere. As with forests, it is a resource we need to protect to keep the carbon out of the air and prevent more warming.

However, with the hotter temperatures, the permafrost is thawing and, as it does so, it releases the greenhouse gases methane and CO₂. (The gases are released because microbes in the soil start to decompose plant material as it thaws.)

It is estimated that by restricting our emissions and the temperature rise to 1.5°C, we would save about 2 million km² of permafrost over several centuries, and avoid the release of the greenhouse gases.^cb

A few more impacts of permafrost thaw are outlined below.

• When the temperature rises due to the permafrost thawing, it causes more permafrost to thaw, which releases more gases, increasing the temperature even more, and so on, in a positive feedback loop.
• The methane released from the permafrost as it thaws also contributes to extensive wildfires. These release even more greenhouse gases into the air to add to warming and also pollute the air thousands of miles away.^a.i
• When the ice in permafrost melts, the ground becomes unstable, which can cause landslides and floods.^e.i. Buildings, roads, power lines and other infrastructure are being damaged by the ground collapsing beneath them. Many people in Alaska and Russia are being forced to move from their homes.^a.i
• In parts of Canada and Alaska the coastline is also becoming eroded and the sea is encroaching on coastal towns. This is happening because of the combined effect of softer thawed permafrost ground and the loss of sea ice. The sea ice used to protect the coasts from storms by acting as a wave-break, but now the soft ground is more exposed to the force of the storms. It is possible for one storm to erode 20 metres of the coastline.^a.i Many coastal communities in Alaska have had to move from their homes, and many more are at risk of being displaced by coastal erosion.

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Oceans are becoming hotter and more acidic ▼

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Extreme weather ▼

Globally the average temperature has risen by 1.2°C above pre-industrial levels, but this rise is not uniform across the world. Average temperatures over land are higher than over the ocean, and most land areas have experienced higher temperatures than the global average. The area that has warmed the fastest is the Arctic, where the annual average temperature is now 2-3°C above its pre-industrial temperature, and 1-2°C above the global average warming. Around one third of people (20-40%) live in regions where warming has already exceeded 1.5°C in at least one season.

As the earth warms the patterns of rainfall also change so that some areas have a lot more rain, and others receive much less. This can lead to floods in some regions of the world and droughts, heatwaves and fires in others. Global average rainfall is increasing since the warmer air can hold more water, but rainfall in some areas may be reduced by changes in wind patterns .

Increased preparedness by disaster management agencies is helping to combat extreme weather events. Many lives are saved by evacuating people in advance. But the devastation and destruction to land and property can be such that people are unable to return to their homes afterwards. In 2019 almost 24 million more people were displaced by climate-related disasters, and a few million people were still displaced at the end of the year. The majority of displacements were in Africa and Asia, but more than 1.5 million were from the Americas and Europe.^idmc

While additional preparation helps to save lives, there is a growing number of people affected in other ways. These include injuries, loss or disruption of livelihoods, particularly in agriculture, and the consequences of this, such as more poverty, malnutrition and hunger.^undrr

Natural hazards such as these have always occurred, but the warming planet has increased either the frequency or intensity, or sometimes both. In the last 20 years, the number of climate-related disasters increased by about 80% compared to the previous 20 years.^undrrr