[Interview file] Another anomaly brought about by climate change,'heatwave on the lake'

Not long ago, the UN conducted a public opinion survey on climate change.

It was a survey called "People's Climate Vote" led by the United Nations Development Program (UNDP), the largest public opinion survey ever with 1.2 million people around the world.

As a result of the survey, about 60% of respondents found that climate change is a global emergency.

The world has recognized and responded to the problems of climate change, such as Joe Biden's declaration of return to the Paris Agreement and Korea's 2050 carbon neutrality, but it is true that climate change is still difficult for us to experience.

This is because the global average temperature rose 1.2℃ in 2020 compared to pre-industrial (1850-1900), but we cannot feel the body ailments that the earth suffers.

In particular, since the temperature change in the water sphere such as the ocean is slower than that of the atmosphere, our perception of this field is bound to be less sensitive.

In the future, more research and response policies are needed.

relation to climate change, relatively active research has been conducted on the atmosphere and the ocean.

However, research on fresh water such as lakes was lacking, and a research team from abroad recently published a study on how climate change affects lakes.

The research team used the concept of lake heatwave* for the first time in this study, and presented the results that heat waves occur frequently in lakes and are sensitive to climate change.

The study studied future data from 1901 to 2099 using satellite observations and computer programs, models, of 702 lakes around the world.

As a result, it was found that lake heatwaves get longer and hotter by the end of the 21st century.

Looking at specific figures, in RCP 8.5**, where greenhouse gas reduction rarely occurs among climate change scenarios, the intensity of heatwave is expected to rise from 3.7℃ to 6.2℃ in 2100.

In addition, the number of heatwave days is expected to increase by 17 times from the current annual average of 7.7 days to 130.8 days in 2100.

The research team predicted that even in RCP 2.6, a scenario in which greenhouse gases were significantly reduced, the intensity of the heatwave would increase significantly to 4.2℃ and the number of heatwave days to 34.6 days.

Experts analyze that lakes are smaller than the ocean and react more sensitively to climate change because of the surrounding land-bound environment.

In fact, from 1985 to 2009, the global average temperature changed by 1℃ for 100 years as the lake temperature increased rapidly, such as 0.74℃/10 ​​years in high latitude and 0.34℃/10 ​​years in low latitude, even in the data observed for 235 lakes around the world. The rise was much steeper than the rise (O'Reilly et al., 2015).

*Lake heatwave: The temperature of the lake is within the top 10% of the average temperature for a specific period (1970-1999) at the time of observation. Lasts more than 5 days.

-It is understood as a lake heat wave or lake heat wave, but it was covered in the article by literally translating it as'lake heat wave' for better understanding.

**RCP: Representative Concentration Pathway, Future Estimation of Greenhouse Gas Concentration

-RCP 2.6 is a scenario where a lot of greenhouse gas reduction has been achieved, and RCP 8.5 is a scenario where there is little reduction of greenhouse gas

We experience heat waves in the summer.

The Korea Meteorological Administration issues a heat wave warning when the highest temperature perceived per day is expected to exceed 33℃ to inform the public of the danger.

As everyone may have experienced, outdoor activities are difficult during a heat wave and the stress level increases, and long exposures are fatal to health.

Fortunately, such a heat wave is limited to a time in summer, and after summer, cool autumn comes.

But what if this heat wave lasts all four seasons?

There will be a terrible thing just imagining, such as a surge in heat patients nationwide.

Fortunately, this situation is still only an imagination for us.

The lake is different.

The research team predicted that in the future due to climate change, heatwave conditions will continue throughout the year in some lakes.

This permanent heatwave condition did not exist before 2000, but it has been shown to occur gradually in the 21st century.

In particular, in the RCP 8.5 scenario, as many as 81 out of the 702 lakes surveyed by the research team turned into permanent heatwave conditions by 2100.

The RCP 2.6 scenario, in which greenhouse gas emissions have been significantly reduced, is also expected to have a permanent heat wave.

<Refer to the picture>

By region, the temperature of the lake varies greatly in high latitudes and relatively little in low latitudes.

The research team predicted that the more intense the heat wave would come for lakes located at high latitudes.

The lake has a topographic environment surrounded by land on all sides.

As such, it has a great influence on many aquatic species and living organisms in the surrounding land.

We provide agricultural water, and there are also people looking for food in the lake.

As such, lakes are an important element in ecosystems and our lives.

What will happen when the temperature of such a lake rises and becomes a heat wave?

First, the system of many ecological species based on lakes is bound to collapse.

In particular, aquatic species living in lakes are more susceptible to climate change.

This is because the space that can be moved to avoid climate change is extremely limited inside the lake.

In addition, as algae generated at elevated temperatures increase rapidly, damage can be accelerated by reducing oxygen (DO, dissolved oxygen) in the water.

Experts predict that the number of green algae will increase by about 20% in the future due to climate change, and among them, species such as cyanobacteria that emit toxins will increase by more than 5%, which will adversely affect the ecosystem.

The problem is more serious not only for fish living in the water, but also for amphibians and reptiles that used their surroundings and lakes as their home.

Amphibians that breathe through the skin are particularly sensitive to climate change, and for this reason, they were selected as'the most likely species to become extinct due to climate change' by the International Union for Conservation of Nature (IUCN).

When those who play a role in the food chain disappear, biodiversity and the entire ecosystem will collapse.

The natural and earth systems interact organically in all fields to the extent that it is difficult to calculate.

Lakes account for 3.7% of the world's land area, but if this little cogwheel breaks down, nature and the consequences we have to bear will be difficult to reverse and unacceptable.

R. Iestyn Woolway*, Eleanor Jennings, Tom Shatwell, Malgorzata Golub, Don C. Pierson & Stephen C. Maberly, "Lake heatwaves under climate change", nature(2021) 589, 402–407, doi.org /10.1038/s41586-020-03119-1