Publié le April 28, 2021
One of the most obvious consequences of climate change is rising temperatures.
It’s quite simple: as the greenhouse effect increases, average air temperature increases. This translates into more hot days and fewer cold days every year. As the graph below illustrates, the annual temperature distribution curve is shifting to the right.
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+1°C is bad enough already. In the Northern Hemisphere:
We have also witnessed periods of extreme heat or heat waves. They are deadly for the most fragile and even threaten much of the population. There’s a certain threshold above which the human body can no longer regulate its own temperature. The 2003 heatwave in Europe resulted in 70,000 deaths within a few weeks.
Not only does the air heat up; average water temperature also increases. Oceans absorb more energy due to the greenhouse effect and their temperatures rise, causing marine life to suffer.
+1°C is bad enough already. For example:
The water cycle is more familiar to the general public than the carbon cycle. Water (H2O) molecules circulate between different environments, in liquid form, such as rain, rivers and seas; solid form, such as snow and ice; or gaseous form, such as steam.
Like other cycles, when it functions naturally the quantity of water on a global scale is stable and sustainable, at around 1,400 billion km3 of water. Evaporation, condensation, precipitation, infiltration and runoff are the well-known stages in the water cycle.
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Humans interact directly with water, but this has a negligible effect on the cycle. Water only remains in the atmosphere for 10 days, compared to around one hundred years for carbon. Even when human-induced water vapor emissions increase, they barely impact the greenhouse effect or global warming.
That said, if human activity does not have a direct effect, the global warming induced by human activity has a direct and disruptive effect on the water cycle.
Atmospheric water storage capacity varies depending on temperature. With heat, there is greater evaporation and the quantity of water stored as vapor increases. As a result, rain is more abundant and there is an increase in the frequency and intensity of heavy precipitation, particularly in mid-latitudes and tropical regions.
+1°C is bad enough already. For example:
Warmer air can contain more water vapor. The atmosphere becomes more humid as temperatures rise.
An already-formed cyclone can draw additional energy from a more humid atmosphere and gain in force. Increased humidity reinforces cyclonic rains, which intensify these extreme weather events.
+1°C is bad enough already
Climate catastrophes are increasingly devastating for populations. Cyclones Sandy (2012) and Irma (2017), and hurricane Harvey (2017) came at a terrible human cost.
Ice is found on glaciers, ice caps and ice shelves. Although all regions with ice are melting more rapidly due to global warming, the consequences are different.
Let’s look at some definitions.
Here, ice rests on land - on a mountain top, for example. It functions like a fresh water reservoir. Glaciers melt during the summer to feed the springs that feed the streams and rivers, and so on. And in winter, under normal conditions, snowfall freezes and transforms into ice, reforming glaciers.
Ice caps are vast frozen areas, sheets of ice with a surface area of less than 50,000 km2 which cover land. They are like very big glaciers.
If they are larger than 50,000km2, they are known as “ice sheets”. The ice can be several thousand meters high.
On our planet, there are only two ice sheets:
Ice shelves are also significant layers of ice. The major difference with an ice cap is that they appear on the surface of water. Ice shelves float, a bit like ice cubes. They are only found in the Arctic and Antarctic.
Now that we’re clear on the definitions, let’s take a look at the effects of temperature increases caused by climate change on ice regions.
Currently 3% of the Earth’s water is fresh water, and only 1% of that is in liquid form. Melting glaciers have an impact on fresh water reserves. In fact, a glacier is supposed to melt gradually during dry periods and run off into streams. By melting more quickly, glaciers no longer act as reservoirs which gradually release fresh water under normal conditions.
Fresh water is drinkable making it necessary for humans and animals on a daily basis. Accelerated melting and the disappearance of glaciers leads to what is known as “water stress” - demand outweighs the quantity available. This is a vital issue that already presents a major geopolitical challenge in some of the world’s driest regions.
Today, nearly all glaciers have lost mass and many hundreds have disappeared completely.
Let’s bust a myth: When ice shelves melt, sea and ocean levels do not rise. Ice shelves float on water, so when they melt, the total water volume does not change. Exactly like an ice cube in a glass of water.
Actually, rising water levels is linked to three different phenomena:
When the ice caps and sheets melt, fresh water is added to the sea and ocean water. Consequently, the water mass increases automatically.
Ice sheets are thousands of meters thick so if they melted completely, ocean levels would rise:
As we have already seen, glaciers store water in ice form. When they melt, the water runs off and joins the rivers that feed into the ocean. This causes water levels to rise.
In addition, glacier melt increases the risk of flooding and landslides, by releasing abnormal water volumes which flow over and destabilize the ground.
Water’s capacity to expand depends on its temperature. When water reaches 20°C over tens of meters, it expands. The volume of water on the planet is colossal – 71% of its surface with an average depth of 4,000 meters. Even a small expansion would have a significant impact on a planetary scale. It is extremely complex to model the rise in water due to expansion.
These are the three climate disruption phenomena which cause rising water levels.
Another consequence of climate change is ocean acidification.
We have seen that CO2 can dissolve in the ocean, like sugar in water. During this chemical reaction, it transforms into carbonates (HCO3- and CO32-) and releases H+ ions. The ions are acidic, and they reduce pH (measure of acidity). Accordingly, the more CO2, the more acidic the ocean becomes.
Note that there is no direct link between water temperature and acidification. The ocean is not becoming more acidic because it is warming up. However, the drop in pH is a direct result of the increased concentration of CO2 in the atmosphere which is in contact with the ocean. Remember, 35% of human-induced CO2 emissions will be directly absorbed by the ocean.
With the drop in the ocean’s pH, “calcification” - the formation of calcium carbonate - becomes more difficult. There are fewer bicarbonate ions which are needed to form calcium carbonate.
More specifically, micro-organisms such as pteropods and coccolithophores usually have calcium carbonate shells or scales. They are significantly affected by ocean acidification. These micro-organisms are the base of the entire marine food web. If they disappear, all marine flora and fauna will be impacted. The ricochet effect will be that whole fishing areas will be depleted of their stocks, jeopardizing food security for some populations.
The IPCC summarizes it as follows: “Changes to water chemistry and temperature are already disturbing species at all levels of the marine food web. This has repercussions on marine ecosystems and the populations which depend on them.”
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