How is climate change affecting our weather?
Source: NASA: Global Climate Change, The Effects of Climate Change
Scientists have high confidence that global temperatures will continue to rise for decades to come, largely due to greenhouse gases produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), which includes more than 1,300 scientists from around the world forecast a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century.
So, the Earth's average temperature has increased about 2 degrees Fahrenheit during the 20th century. What's the big deal?
Two degrees may sound like a small amount, but it's an unusual event in our planet's recent history. Earth's climate record, preserved in tree rings, ice cores, and coral reefs, shows that the global average temperature is stable over long periods of time. Furthermore, small changes in temperature correspond to enormous changes in the environment.
For example, at the end of the last ice age, when the Northeast United States was covered by more than 3,000 feet of ice, average temperatures were only 5 to 9 degrees cooler than today. According to the IPCC, the extent of climate change effects on individual regions and countries will vary over time and will challenge different societal and environmental systems to mitigate or adapt to change. "Taken as a whole," the IPCC states, "the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time."
Some of the effects of global climate change are as follows:
1. Temperatures Will Continue to Rise.
Source: National Ocean and Atmospheric Administration NOAA
Because human-induced warming is superimposed on a naturally varying climate, the temperature rise has not been, and will not be, uniform or smooth across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling. According to the NOAA 2019 Global Climate Summary, the combined land and ocean temperature has increased at an average rate of 0.07°C (0.13°F) per decade since 1880; however, the average rate of increase since 1981 (0.18°C / 0.32°F) is more than twice as great.
Changes in global average surface temperature from 1990-2019. Places that warmed by up to 1° Fahrenheit over the past 30 years are red, places that have cooled by up to 1° F are blue, and places where we don't have enough observations to calculate a trend are light grey. NOAA Climate.gov map, based on NCEI data.
The 10 warmest years on record have all occurred since 1998, and 9 of the 10 have occurred since 2005. The year 1998 is the only year from the twentieth century still among the ten warmest years on record. Looking back to 1988, a pattern emerges: except for 2011, as each new year is added to the historical record, it becomes one of the top 10 warmest on record at that time, but it is ultimately replaced as the “top ten” window shifts forward in time.
In 2020, models project that global surface temperature is more than 0.5°C (0.9°F) warmer than the 1986-2005 average, regardless of which carbon dioxide emissions pathway the world follows. This similarity in temperatures regardless of total emissions is a short-term phenomenon: it reflects the tremendous inertia of Earth's vast oceans. The high heat capacity of water means that ocean temperature does not react instantly to the increased heat being trapped by greenhouse gases. By 2030, however, the heating imbalance caused by greenhouse gases begins to overcome the oceans'; thermal inertia, and projected temperature pathways begin to diverge, with unchecked carbon dioxide emissions likely leading to several additional degrees of warming by the end of the century.
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2. Changes in Precipitation Patterns
Much of the public discussion around climate change has focused on how much the Earth will warm over the coming century. But climate change is not limited just to temperature; how precipitation – both rain and snow – changes will also have an impact on the global population.
While the models used by climate scientists generally agree on how different parts of the Earth will warm, there is much less agreement about where and how precipitation will change.
With higher temperatures comes greater evaporation and surface drying, potentially contributing to the intensity and duration of drought. However, as the air warms its water- holding capacity increases, particularly over the oceans. According to the Clausius-Clapeyron
equation, the air can generally hold around 7% more moisture for every 1C of temperature rise. As such, a world that is around 4C warmer than the pre-industrial era would have around 28% more water vapour in the atmosphere. But this increased moisture will not fall
evenly across the planet. Some areas will see increased precipitation, while other areas are expected to see less due to shifting weather patterns and other factors.
The figure below shows projected percentage change in precipitation between the current climate (represented by the 1981-2000 average) and the end of the century (2081-2100) in the average of all of the climate models featured in in the latest Intergovernmental Panel on Climate Change (IPCC) report (CMIP5), using the high-end warming scenario (RCP8.5). Purple colours show areas where precipitation will increase, while orange areas indicate less future rain and snow.
On average, warming is expected to result in dry areas becoming drier and wet areas becoming wetter, especially in mid- and high-latitude areas. (This is not always true over land, however, where the effects of warming are a bit more complex.)
The average of the models shows large increases in precipitation near the equator, particularly in the Pacific Ocean. They also show more precipitation in the Arctic and Antarctic, where cold temperatures currently limit how much water vapour the air can hold. The Mediterranean region is expected to have around 20% less precipitation by 2100 in an RCP8.5 world, with similar reductions also found in southern Africa. Western Australia, Chile, and Central America/Mexico may all become around 10% drier.
However, the simple picture painted by the average of all the models shown above hides profound differences. There are actually relatively few areas that all the models agree will become wetter or drier. Climate models are not perfect and projections of future average precipitation changes may become more consistent as models continue to improve.
While models disagree on how average precipitation will change in many parts of the world, there are some areas where nearly all the models tell the same story about future changes. The figure below shows the same annual average change in precipitation between today and the end of the century but adds dots to indicate areas where at least nine out of 10 models agree on the direction of change.
Here there is widespread agreement among the models that both the tropical Pacific and high-latitude areas will have more precipitation in the future. India, Bangladesh and Myanmar will all become wetter, as will much of northern China.
The models largely agree that the Mediterranean region and southern Africa will have less precipitation in the future. They also agree on reduced precipitation in southwest Australia around Perth, in southern Chile, the west coast of Mexico and over much of the tropical and
subtropical Atlantic ocean.
When looking at projected seasonal changes, in winter there are greater reductions in precipitation projected over northern Africa, but no agreement on increases in precipitation over India or much of South Asia. In spring, models agree that southern California will experience less rainfall. In summer, reductions in precipitation in southern Africa are particularly strong, while in autumn increases in rainfall over India, Bangladesh and the Sahara region all stand out.
Models also generally agree that precipitation, when it does occur, will become more intense nearly everywhere. Unlike average annual precipitation, almost the entire world is expected to see an increase in extreme precipitation as it warms. Models suggest most of the world will have a 16-24% increase in heavy precipitation intensity by 2100 leading to more flooding and landslides. In other, words, heavy rain is likely to get heavier especially in Central Africa and South Asia. A warmer world is also projected to increase soil evaporation and reduce snowpack, exacerbating droughts even in the absence of reduced precipitation. Less snowpack will have complex effects on mountain streams and river flows and all life that has relied on constant mountain water flows from annual ice thawing.
3. More Droughts and Heat Waves
When heat waves prolong, there is an important negative feedback that amplifies drought and heat and sets the stage for wildfires. In these cases, the prevailing conditions dry out the land, the vegetation is wilted or crisp dry, and all of the heat from the sun goes into
raising temperatures at which point a simple spark will set the dry land alight. Ordinarily, the process of evaporative cooling, surface water or wetness acts as an evaporative cooler on land and reduces the chance of fires, but droughts remove this natural barrier against
Droughts and heatwaves not only have a negative impact on agriculture and forestry and the associated livelihoods of farmers, but also severally impacts birds, animals and plant life, indeed all the biodiversity that survives in these environments.
In 2020 wildfires in Australia and USA were particularly damaging. In Australia, 104 m acres of land was burnt, 34 people died, 3 billion animals were affected of which 1 billion died (including 1/3 of the koala population), emitted 306 million tonnes of CO2 (estimated by NASA) and cost about A$2 billion. The fires took 9 months to burn out and 26% of Australian businesses say they were affected by it. California experienced the largest wildfire season recorded in modern data. 4.2 m acres were destroyed, 12,000 homes and structures, 7 people died, and the total economic cost is estimated at US$200bn.
4. Hurricanes Will Become Stronger and More Intense
The intensity, frequency and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s as sea temperatures have increased. According to a paper published in Nature in November 2020, in the 1960’s hurricanes lost on average 75% of their intensity within 24 hrs of landfall, today this is only 50%.
Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.
5. Sea Level Will Rise 1-8 feet by 2100
The ocean is vast, covering 140 million square miles (363 million square km), equivalent to approximately 72 per cent of the earth's surface. According to the UN more than 600 million people (around 10 per cent of the world’s population) live in coastal areas that are less than 10 meters above sea level. And nearly 2.4 billion people (about 40 per cent of the world’s population) live within 100 km (60 miles) of the coast. Oceans, coastal and marine resources are very important for people living in coastal communities, who represent 37 per cent of the global population in 2017. But our oceans are being severely impacted by climate change. Global sea level has risen by about 8 inches since reliable record keeping began in 1880. It is projected to rise another 1 to 8 feet by 2100.
In the next several decades, storm surges and high tides could combine with sea level rise and land subsidence to further increase flooding in many regions.
Sea level rise is caused primarily by two factors related to global warming: the added water from melting ice sheets and glaciers and the expansion of seawater as it warms. The graph below from NASA tracks the change in sea level since 1993 as
observed by satellites.
Sea level rise will continue past 2100 because the oceans take a very long time to respond to warmer conditions at the Earth’s surface. Ocean waters will therefore continue to warm and sea level will continue to rise for many centuries at rates equal to or higher than those of the current century. As 600 million people live in areas less than 10 metres above sea level climate change will inevitably create millions of climate refugees. Where will they go?
6. Bleaching of coral, effects of sea temperature rising
Over half a billion people depend on reefs for food, income, and protection. According to the Natural History Museum in the UK, coral reefs have an estimated global value of £6 trillion each year, due in part to their contribution to fishing and tourism industries and the coastal protection they provide. More than 500 million people worldwide depend on reefs for food, jobs and coastal defence. Coral reefs teem with diverse life. Thousands of species can be found living on one reef alone. The ridges in coral reefs act as barriers and can reduce wave energy by up to 97%, providing crucial protection from threats such as tsunamis. They help protect areas such as mangrove forests and seagrass beds that act as nurseries for marine animals, as well as human coastal populations. Extracts from animals and plants living on reefs have been used to develop treatments for asthma, arthritis, cancer and heart disease.
But all this is under threat. Coral reefs bleach and die with rising sea temperatures and are destroyed in cyclones and severe storms. They
require time to recover but the increasing frequency of extreme weather events on our coasts is making this harder to naturally occur.
7. Arctic Likely to Become Ice-Free
The extent of sea ice is affected by winds and ocean currents as well as the sea temperature. Since the satellite record began in 1978, the yearly minimum Arctic sea ice extent (which occurs in September) has decreased by about 40% of its area and up to 70% of its volume, making it one of the clearest signs of human-caused global heating.
Ice cover expands again each Arctic winter, but the ice is thinner than it used to be because it cannot make up for volume loss in the warmer annual cylces. A new Nature Climate Change study predicts that summer sea ice floating on the surface of the Arctic Ocean could disappear entirely by 2035. Until relatively recently, scientists did not think we would reach this point until 2050 at the earliest. The loss of the ice exposes the dark ocean, which absorbs more of the sun’s heat and further ramps up temperatures. These changes are also being increasingly linked to more extreme weather including severe winters, deadly summer heatwaves and
torrential floods at lower latitudes such as in Europe and the US.
8. Siberian Perma-frost
Arctic permafrost has been diminishing for many centuries. The consequence is thawing soil, which may be weaker, and release of methane, which contributes to an increased rate of global warming as part of a feedback loop caused by microbial decomposition. Wetlands drying out from drainage or evaporation compromises the ability of plants and animals to survive. When permafrost continues to diminish, many climate change scenarios will be amplified.
According to the Intergovernmental Panel on Climate Change, IPCC Fifth Assessment Report there is high confidence that permafrost temperatures have increased in most regions since the early 1980s. Observed warming was up to 3 °C in parts of Northern Alaska (early 1980s to mid-2000s) and up to 2 °C in parts of the Russian European North (1971–2010). In Yukon, the zone of continuous permafrost might have moved 100 kilometres (62 mi) poleward since 1899, but accurate records only go back 30 years. It is thought that permafrost thawing could exacerbate global warming by releasing methane and other hydrocarbons, which are powerful greenhouse gases. It also could encourage erosion because permafrost lends stability to barren Arctic slopes.
Arctic temperatures are expected to increase at roughly twice the global rate. The Intergovernmental Panel on Climate Change (IPCC) will in their fifth report establish scenarios for the future, where the temperature in the Arctic will rise between 1.5 and 2.5 °C by
2040 and with 2 to 7.5 °C by 2100. Estimates vary on how many tons of greenhouse gases are emitted from thawed permafrost soils. One estimate suggests that 110–231 billion tons of CO 2 equivalents (about half from carbon dioxide and the other half from methane) will be emitted by 2040, and 850–1400 billion tons by 2100. This corresponds to an average annual emission rate of 4–8 billion tons of CO 2 equivalents in the period 2011–2040 and annually 10–16 billion tons of CO 2 equivalents in the period 2011–2100 as a result of thawing permafrost. For comparison, the anthropogenic emission of all greenhouse gases in 2010 is approximately 48 billion tons of CO 2 equivalents. Release of greenhouse gases from thawed permafrost to the atmosphere will significantly increases global warming and this may be happening sooner that we had hoped. For further reading on the Artic permafrost situation.
CMIP5 RCP8.5 multi-model average percent change in total precipitation (rain and snow) between 1981-2000 and 2081-2100. Uses one run for each model, 38 models total. Data from KNMI Climate Explorer; map by Carbon Brief.
As first figure, but with areas where 90% of the models agree on the sign of the change highlighted with dots. Data from KNMI Climate Explorer; map by Carbon Brief.