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Study Indicates Global Warming Could Reduce Biodiversity In Tropics

Published in the journal Current Biology, the study estimates that marine biodiversity tends to increase until the average surface temperature of the ocean reaches about 65 degrees Fahrenheit, beyond which that diversity slowly declines

Study Indicates Global Warming Could Reduce Biodiversity In Tropics
Highlights
  • For the study, the researchers went back about 145 million years
  • They compiled estimated temperatures and fossil records of molluscs
  • They got temperature-diversity relationship across 10 geologic intervals

Washington: New research by the University of Nebraska-Lincoln suggests that temperature can largely explain why the greatest variety of aquatic life resides in the tropics but also why it has not always and, amid record-fast global warming, soon may not again. The bulging, equator-belted midsection of Earth currently teems with a greater diversity of life than anywhere else – a biodiversity that generally wanes when moving from the tropics to the mid-latitudes and the mid-latitudes to the poles. Published in the journal Current Biology, the study estimates that marine biodiversity tends to increase until the average surface temperature of the ocean reaches about 65 degrees Fahrenheit, beyond which that diversity slowly declines.

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During intervals of Earth’s history when the maximum surface temperature was lower than 80 degrees Fahrenheit, the greatest biodiversity was found around the equator, the study concluded. But when that maximum exceeded 80 degrees, marine biodiversity ebbed in the tropics, where those highest temperatures would have manifested, while peaking in waters at the mid-latitudes and the poles. Marine life that could travel considerable distances likely migrated north or south from the tropics during periods of extreme heat, said co-author Will Gearty, a postdoctoral researcher of biological sciences at Nebraska.

Stationary or slower-moving animals, such as sponges and sea stars, may have instead faced extinction.

People have always theorized that the tropics are a cradle of diversity — that it pops up and then is protected there, Will Gearty said.

“There’s also this idea that … there’s lots of migration toward the tropics, but not away from it. All of that centres around the idea that the highest diversity will always be in the tropics. And that’s not what we see as we go back in time.”

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Will Gearty, Yale’s Thomas Boag and Stanford’s Richard Stockey went back about 145 million years, compiling estimated temperatures and fossil records of molluscs — snails, clams, cephalopods and the like — from 24 horizontal bands of Earth that were equal in surface area. The trio chose mollusc records for multiple reasons: They live (and lived) around the globe, in large enough numbers to accommodate statistical analyses, with hard enough shells to yield identifiable fossils, with enough variation that their diversity trends might generalize to fish, corals, crustaceans and an array of other marine animals. That data allowed the team to derive the temperature-diversity relationship across 10 geologic intervals that covered most of the elapsed time from the Cretaceous period through the modern-day.

Temperature seems to account for a lot of the trend that we see in the fossil record, Will Gearty said.

“There are certainly other factors, but this seems to be the first-order predictor of what’s going on.”

To investigate why temperature might be so influential and predictive, Richard Stockey took the lead in developing a mathematical model. The model accounts for the fact that higher temperatures generally increase the amount of energy in an ecosystem, theoretically raising the ceiling on the biodiversity an ecosystem can sustain, at least to a point. But it also factors in metabolism and the small matter of oxygen, which, by dissolving in water, makes aquatic life possible in the first place. Colder waters dissolve more oxygen, meaning that elevated temperatures naturally reduce the amount available to marine life and, by extension, potentially limit the biodiversity an ecosystem can support. Higher temperatures also raise the metabolic demands of organisms, increasing the minimum oxygen needed to sustain active marine animals.

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That means you require more oxygen in warmer waters, Will Gearty said.

“And if the amount of oxygen available is not satisfying that increase in metabolism, you won’t survive in that environment. So, to survive, you’ll need to move to another environment where the temperature is lower.”

The team applied its model to numerous marine species with varying metabolisms. As expected, metabolism influenced how the population of a given species would respond to a rise in temperature, along with the temperature threshold beyond which that population would decline. When the researchers averaged the effects of metabolism and oxygen availability across those species, they discovered that the resulting temperature-diversity relationship resembled — and, in doing so, supported — the one they derived from the fossil record.

It shows a similar trend of this (biodiversity) increase and then decreases, Will Gearty said.

“After many a day at the whiteboard just trying to figure out how to make it work, it all just came together very nicely at the end — you know, a nice little bow on top.”

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Collectively, the study indicates that human-driven global warming could hit the inhabitants of tropical waters especially hard. The average surface temperature of tropical waters could jump by as many as 6 degrees Fahrenheit by the year 2300, according to one projection. And according to the fossil records analyzed for the study, similar temperature increases during the past 145 million years have sometimes permanently driven mollusc species from tropical waters. There are worrying signs that the expected trend is already underway, Will Gearty said.

Though the team had difficulty narrowing down the projected magnitude of the decline in biodiversity, Will Gearty said the worst-case projection called for the tropics losing up to 50 per cent of their marine species by 2300. Some of the loss will take the form of migration. Yet the warming could spell doom for, say, corals and the thousands of marine species that they support, he said, as seen in the oft-fatal bleaching of the Great Barrier Reef off the coast of Australia.

This (biodiversity loss) is already happening, and it will only keep happening unless we do something, Will Gearty said.

“We can’t really take back the buildup of carbon dioxide (in the atmosphere) that’s already happened, so it’s going to keep happening for some amount of time. But it’s up to us to determine how long until it’ll stop.”

Also Read: India And United Kingdom Deepen Work To Combat Climate Change By 2030

(This story has not been edited by NDTV staff and is published from a syndicated feed.)

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World

26,78,24,983Cases
22,84,48,447Active
3,40,97,388Recovered
52,79,148Deaths
Coronavirus has spread to 196 countries. The total confirmed cases worldwide are 26,78,24,983 and 52,79,148 have died; 22,84,48,447 are active cases and 3,40,97,388 have recovered as on December 9, 2021 at 3:47 am.

India

3,46,66,241 9,419Cases
94,742 1,009Active
3,40,97,388 8,251Recovered
4,74,111 159Deaths
In India, there are 3,46,66,241 confirmed cases including 4,74,111 deaths. The number of active cases is 94,742 and 3,40,97,388 have recovered as on December 9, 2021 at 2:30 am.

State Details

State Cases Active Recovered Deaths
Maharashtra

66,40,888 893

9,964 157

64,89,720 1,040

1,41,204 10

Kerala

51,78,892 5,038

41,615 887

50,95,263 4,039

42,014 112

Karnataka

29,99,098 399

7,284 155

29,53,565 238

38,249 6

Tamil Nadu

27,32,648 703

7,946 36

26,88,142 728

36,560 11

Andhra Pradesh

20,74,217 181

2,011 3

20,57,749 176

14,457 2

Uttar Pradesh

17,10,502 10

139 7

16,87,452 3

22,911

West Bengal

16,20,803 574

7,576 0

15,93,659 568

19,568 6

Delhi

14,41,514 65

404 28

14,16,010 36

25,100 1

Odisha

10,50,760 255

1,931 11

10,40,403 264

8,426 2

Chhattisgarh

10,07,075 37

341 9

9,93,140 27

13,594 1

Rajasthan

9,54,984 40

236 16

9,45,792 24

8,956

Gujarat

8,27,873 67

417 45

8,17,361 22

10,095

Madhya Pradesh

7,93,288 14

140 1

7,82,619 13

10,529

Haryana

7,71,904 29

223 15

7,61,626 14

10,055

Bihar

7,26,259 9

36 6

7,14,133 3

12,090

Telangana

6,77,546 205

3,871 19

6,69,673 185

4,002 1

Assam

6,18,042 134

2,541 24

6,09,374 158

6,127

Punjab

6,03,578 22

350 0

5,86,614 20

16,614 2

Jharkhand

3,49,383 16

129 7

3,44,113 23

5,141

Uttarakhand

3,44,402 17

192 3

3,36,799 14

7,411

Jammu And Kashmir

3,38,198 151

1,639 38

3,32,070 111

4,489 2

Himachal Pradesh

2,27,753 69

722 14

2,23,174 81

3,857 2

Goa

1,79,307 65

441 37

1,75,478 28

3,388

Mizoram

1,37,377 320

3,049 10

1,33,819 309

509 1

Puducherry

1,29,128 23

230 1

1,27,022 22

1,876

Manipur

1,25,429 23

325 5

1,23,119 28

1,985

Tripura

84,888 14

94 11

83,968 3

826

Meghalaya

84,631 12

240 11

82,916 23

1,475

Chandigarh

65,515 7

67 2

64,628 5

820

Arunachal Pradesh

55,298 3

29 2

54,989 5

280

Sikkim

32,390 8

200 2

31,785 6

405

Nagaland

32,143 1

116 2

31,328 3

699

Ladakh

21,749 14

230 17

21,304 31

215

Dadra And Nagar Haveli

10,683

0 0

10,679

4

Lakshadweep

10,405

11 0

10,343

51

Andaman And Nicobar Islands

7,691 1

3 0

7,559 1

129

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