The color of the Earth is changing, and it's not a good thing...

A few days ago, many netizens said that they felt that the red leaves this year appeared later than in previous years. Coincidentally, according to the British Broadcasting Corporation (BBC), the oak forests in Southamptonshire, England, also stayed green longer this year than in previous years, and seemed to be delayed by about two weeks compared to the previous time when the red and yellow beauty appeared.

Many studies have confirmed that climate change affects not only the timing of leaf change and fall, but also the color of leaves, changing what we perceive as "autumn colors." Not only that, but recent papers have shown that climate change is changing the color of the Earth on a larger scale : the oceans and Antarctica are turning green at an alarming rate.

The autumn colors have changed

In a 2023 paper published in Landscape Ecology, researchers in the United States combined remote sensing data with literature records to analyze the fall foliage conditions in Acadia National Park from 1950 to 2021. They found that the peak of fall foliage has been delayed by about nine days, nearly two weeks, compared to 1950. Based on future climate forecasts, the researchers speculate that by 2060, the best time to see red leaves in Acadia National Park will probably be between October 30 and November 2.

Peak autumn foliage season from 1950 to 2021 (Image source: original paper)

So, what factors cause the change in leaf fall time? Researchers believe that both temperature and precipitation affect the time of leaf fall . For example, since 1950, the average minimum and maximum temperatures in Acadia National Park have risen by more than 1°C; the number of warm nights has increased by an average of 26 days per year, and the number of warm days has increased by an average of 17 days; the number of days with "heavy rains" has also increased by an average of 4 days per year. These may all be related to the delay in leaf fall. Correspondingly, a study published in Nature Climate Change in 2022 also showed that if climate change brings drought instead of increased rainfall, it may lead to earlier leaf aging.

Another study published in Science in 2023 showed that the time of leaf aging is not only affected by factors such as temperature, but also by the length of daylight and photosynthesis in the early growth of leaves.

The study shows that climate warming will have two opposite effects on the time of leaf fall. If the temperature is warmer in spring , the leaves will sprout earlier and grow faster. In autumn, such leaves will begin to age and fall earlier. For every 1°C increase in temperature, the time when the leaves begin to age will be 1.9 days earlier on average. On the contrary, if the temperature is higher in autumn, it will slow down the rate of leaf aging and delay the time when the leaves fall. For every 1°C increase in temperature, the process of leaf aging will be delayed by an average of 2.6 days.

Higher temperatures before the summer solstice will cause leaves to begin aging earlier; higher temperatures after the summer solstice will slow down the aging process of leaves, thus delaying the time of leaf fall. (Image source: original paper)

In addition to the time of leaf fall, climate change will also affect the color of autumn leaves. Leaves contain a variety of pigments. In addition to chlorophyll , carotenoids and anthocyanins are also common. Before the leaves begin to age, chlorophyll will continue to be synthesized and decomposed in the leaves, maintaining a very high level. Therefore, even if carotenoids are present in the leaves at this time, the leaves look green. But in autumn, the anthocyanin content in the leaves increases sharply, the chlorophyll content decreases, and the carotenoid content remains basically stable, and the leaves then show a variety of colors.

Many factors influence the production of anthocyanins, molecules that plants make in high amounts when exposed to strong sunlight and when their sugar levels are high, which is why ripe fruit tends to have brighter colors. If the day is warm and sunny, the leaves make a lot of sugar, and if the nights are cool, the sugars stay in the leaves and promote anthocyanin production. Under these conditions, autumn leaves tend to be brighter and redder. But now, climate change is causing the nights to get warmer, so autumn leaves are becoming duller.

The ocean is green

But the changing colors of fall leaves may not be a big deal for Earth. After all, not every tree species loses its leaves, and the leaf-falling season only takes up a small portion of the year. However, many studies have shown that the color of the ocean is changing at an alarming rate, based on data captured by satellites from space.

In a paper published in Nature in 2023, researchers analyzed data collected by the Moderate Resolution Imaging Spectrometer on satellites over the past 20 years. The results showed that 40% of the world's surface oceans are rapidly turning green. Especially in tropical waters near the equator, the rate of greening is particularly fast. This phenomenon shocked scientists because although scientists had expected the ocean to gradually turn green, they never thought it would be so fast. They thought it would take 40 years or even longer.

Measurements of ocean color from the satellite's Moderate Resolution Imaging Spectroradiometer (Image credit: NASA and Joshua Stevens, using Landsat data from the US Geological Survey and MODIS data from LANCE/EOSDIS Rapid Response)

The color of the ocean has a lot to do with the phytoplankton and algae in it. The rich chlorophyll in these organisms will appear green. Researchers speculate that the ocean may turn green because the distribution of nutrients in the ocean has changed. For example, climate change has caused the surface layer of the ocean to warm up, and the ocean has become stratified. There is less material exchange between the deep and surface layers, so it is more difficult for nutrients to rise from the deep to the surface. In the absence of nutrients, smaller phytoplankton and algae may be more likely to survive than other phytoplankton, which may cause the color of the ocean to change.

Antarctica is green too

In addition to the ocean, the color changes in Antarctica are also very obvious. A study published in Nature Geoscience in October this year showed that satellite observations showed that due to climate warming, the Antarctic Peninsula has generally turned green in recent decades: from 1986 to 2021, the vegetation (including mosses, lichens, leaf mosses and algae) on the Antarctic Peninsula has increased from 0.863 square kilometers to 11.947 square kilometers, an increase of nearly 14 times in 35 years. Moreover, the speed of greening is getting faster and faster, and the greening rate after 2016 is 30% higher than before.

The greening of the Antarctic Peninsula (Image source: original paper)

Since 1950, the temperature on the Antarctic Peninsula has risen by nearly 3°C. Although most of the vegetation on the Antarctic Peninsula is moss, researchers believe that the spread of moss will also increase the surface soil of the Antarctic Peninsula, which may lay the foundation for the survival of other vegetation. What is more worrying is that since the native plants here have been living in a relatively stable extreme environment, if other species invade, it is likely that the native plants will find it difficult to survive the competition . Therefore, the fragile Antarctica may undergo fundamental changes from now on.

Climate change is reshaping the Earth's ecosystems. The fading colors of autumn leaves, the greening of the oceans, and the expansion of vegetation in Antarctica may seem subtle, but they are a microcosm of the widespread impact of climate change on the natural world. The "autumn colors" we are familiar with may no longer exist, replaced by a gradually greening Earth. In the face of this reality, perhaps it is more important for us to appreciate nature while cherishing and actively protecting this beauty and fragility. Climate change is not a distant future, but a present that we cannot avoid.

References

[1]https://www.bbc.com/news/articles/cx2ng2x81ndo

[2]https://link.springer.com/article/10.1007/s10980-023-01703-0

[3]https://www.nature.com/articles/s41558-022-01464-9

[4]https://www.science.org/doi/10.1126/science.adf5098

[5]https://www.fs.usda.gov/visit/fall-colors/science-of-fall-colors

[6]https://www.climatecentral.org/climate-matters/fall-foliage-and-climate-change

[7]https://www.nature.com/articles/s41586-023-06321-z

[8]https://www.nature.com/articles/d41586-023-02262-9

[9]https://www.nature.com/articles/s41561-024-01564-5

[10]https://www.nature.com/articles/d41586-024-03219-2

Planning and production

Source: Global Science (ID: huanqiukexue)

Author: Huang Yujia

Editor: Yang Yaping

Proofread by Xu Lai and Lin Lin