- More CO2 in the atmosphere
The increase in the amount of greenhouse gases in the atmosphere recorded since 1750 is associated with human activities. Since the report released in 2014, CO2 concentrations, for example, have risen to an annual average of 410 ppm (parts per million). There was no such concentration for at least 2 million years. And the greenhouse gases methane and nitric oxide are higher than at any time in 800,000 years.
Since 1750, the concentration of CO2 has increased by 47%, while the concentration of methane has increased by 156%. It is because of the growth of these indicators that the IPCC has repeatedly indicated in its report that climatic changes are caused by human activity.
According to the latest figures from the National Oceanic and Atmospheric Administration, the climate authority under the US Department of Commerce, CO2 has now climbed to 419 ppm.
- It's getting warmer
The average global temperature between 2011 and 2020 was about 1.09 degrees higher compared to the period from 1850 to 1900 - the pre-industrial era. The general rise in temperature also hides large regional differences. The temperature has increased especially strongly in the Arctic, and this process will continue. Humans are responsible for 1.07 degrees of warming, which is almost everything. Its impact is mainly due to CO2 emissions.
The temperature rises more over land than over the sea. Overland, the warming is 1.6 degrees, over the sea - 0.9 degrees.
Temperatures will rise even more in the future. If we fail to significantly reduce greenhouse gas emissions, it will become more than 1.5-2 degrees warmer over the 21st century. The purpose of the Paris Agreement is to prevent this. If it is possible to reduce CO2 emissions, then, under the most optimistic scenarios, it is unlikely that the temperature will rise by more than 2 degrees over the 21st century. On the other hand, an increase of 2 degrees may occur as early as 2041-2060 - it depends on how much CO2 is released into the atmosphere.
According to the most optimistic estimate of greenhouse gas emissions, the temperature in 2081-2100 will be 1-1.8 degrees higher than the pre-industrial level, and under the most pessimistic scenarios it will rise by 3.3-5.7 degrees.
The last time the temperature on Earth was more than 2.5 degrees above the level of the pre-industrial era more than 3 million years ago. And over the past 2000 years, it has never risen faster than from 1970 to the present.
- Sea level is rising
The global mean sea level rose 20 centimeters from 1901 to 2018. This is faster than at any time in the past three thousand years. The trend is increasing.
For example, from 1901 to 1971, the water level rose by about 1.3 mm annually, and from 2006 to 2018 it is already growing by 3.7 mm per year. The rise in sea level is almost certainly caused by human-related CO2 emissions. It is very likely that the water level will continue to rise throughout the 21st century.
According to the most optimistic scenarios, the water level by 2100 will rise by half a meter compared to today. In the worst case - by a meter. It cannot be ruled out that by 2150 it will rise by five meters, but it is not yet completely clear how the glaciers will react to warming.
From the point of view of the history of the Earth, sea-level rise is not unusual. 125,000 years ago it was probably 5-10 meters higher than it is today, and 3 million years ago it was 5-25 meters. In some areas near land with high levels of icing, such as around Greenland, water levels are predicted to fall.
- The sea will heat up
Sea temperatures at depths of up to 700 meters have been rising since the early 1970s - quite possibly due to human activities. Until the end of the 21st century, the temperature will rise at best twice and at worst - eight times faster.
In the past century, the world's oceans have warmed faster than at any time since the last ice age 11,000 years ago.
- More rainfall on the planet
Since the 1950s, the average amount of precipitation on the planet has increased, and since the 1980s, this trend has only intensified. However, this process varies greatly across regions. For example, there will be less rainfall in the Mediterranean region, Western Australia and southwestern South America in the future. But in the equator in the Pacific Ocean, in Northeast Africa, including the Sahara, and in the Arctic, there will be more of them.
- Sea ice will disappear in the north
Human impact is probably the main reason for the decline in sea ice in the Arctic when comparing 1979-1988 with 2010-2019. Sea ice has decreased by 40% when comparing these two periods in September (end of summer), and by 10% when comparing them in March (end of winter).
Between 2011 and 2020, the average annual sea ice area in the Arctic declined to its lowest since 1850. Probably, they have become the least in at least the last thousand years.
In Antarctica, this trend is practically not observed in the period from 1979 to 2020.
- Glaciers retreat
The anthropogenic impact is also cited as the main reason that the area of glaciers around the world has been shrinking since the 1950s. Globally, the decline in glaciers is now most noticeable for at least 2 thousand years.
Glacier melting is predicted to continue in the future, even if global temperatures stabilize. Glaciers in Greenland and Antarctica will suffer, for example.
- The Gulf Stream is weakening
The chances that the glacier will instantly disappear and the sea currents change dramatically is low. But it is very likely that the Gulf Stream, which among other things provides a warmer climate in Northern Europe, including Denmark, will weaken in the 21st century, even if emissions of greenhouse gases into the atmosphere are minimal.
This probably will not lead to the complete disappearance of the current by 2100. But if this does happen, the climate in Northern Europe will become colder, and the tropical rain belt will move further south. Asian and African monsoon rains will weaken, while in the southern hemisphere it will intensify.
- There will be more extreme weather events
It is very likely that extreme heat is now common in almost all land regions since 1950. But there are fewer periods of extreme cold, and the temperature is no longer falling so low.
Both are likely to be caused by human activity. For example, in the Pacific Ocean, powerful cyclones and hurricanes have become more frequent, which go further north.
Every half a degree of further global warming will increase both extreme temperatures and the intensity of unusually powerful precipitation. Droughts will also worsen.
- Large impacts of climate change
The trend towards more extreme weather will continue as warming climates will spill over into increasingly intense periods of very humid and very dry weather. Where and how often this will occur depends on changes in the global wind rose, including monsoon and hurricane belts.
With a 1.5-degree rise in temperature, extreme rainfall and flooding will intensify and occur more frequently in most parts of Africa, Asia, North America, and Europe. If the temperature rises by 2 degrees, this trend will become even more noticeable, and, for example, droughts will occur more often in Africa, South America, and Europe, which will have a negative impact on agriculture.
Urban development also contributes to increased rainfall and flooding.
Read the original text at Jyllands-Posten