Planet greening negated global warming, show NASA maps - Pragnya IAS Academy - News Analysis.

Planet greening negated global warming, show NASA maps.

Since 2000, at least 30% of areas with more leaf coverage were cooled by it, the research noted

The greening of the planet changed the movement of air near the land surface between 2000 and 2014 in ways that offset some warming, the United States National Aeronautics and Space Administration (NASA) has shown in its latest maps.

Remote sensing scientists from at the Boston University had found in 2019 that vegetation cover increased globally by five per cent since the early 2000s. In 2020, the group showed that increase in greenness led to a slight offset in global temperatures. This study was published in Science Advances.

The planet has been getting greener in the last 40 years. Until now, scientists believed vegetation could alter temperatures at the surface by the way the leaf area changed how much sunlight it absorbed or reflected. More greenery can also change how well water can penetrate and be retained by soil and leaves.

In the latest research, however, scientists found that the strongest cooling effect was how the increasing leaf cover led to increased or decreased drag and turbulence in the air above. This meant that the aerodynamic resistance was less with more vegetation.

Trends in the leaf area index (LAI) around the world from 2000 to 2014. LAI is a measure of the amount of leaf area relative to ground area during the growing season. Source: NASA

Extra leaves, according to the researchers, can allow more heat and water vapor to rise into the atmosphere. Extra leaves may also increase the amount of water transpired by plants, thereby allowing even more water to be transferred. The moisture helps carry away a significant amount of heat from the ground level and lead to cooler surfaces.

The researchers found that since 2000, at least 30 per cent of areas with more leaf coverage were cooled by it, while 5 per cent have grown warmer.

Chi Chen, one of the authors of the study, said: “In the fight against climate change, plants are the lonely-only defenders. Stopping deforestation and ecologically sensible large-scale tree-planting could be one simple, but not sufficient, defense against climate change.”

The authors noted, however, that the cooling effect from extra vegetation was large from an energy dissipation perspective, but wa quite small compared to the pace and intensity of global warming. (Source: downtoearth)

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Planet greening negated global warming, show NASA maps.

Global warming will lead to river ice cover decline: Study - Pragnya IAS Academy - News Analysis.

Global warming will lead to river ice cover decline: Study.

The annual river ice cover will decline by about six days for every one degree Celsius increase in global temperatures, posing economic and environmental consequences, according to a study. The research, published in the journal Nature, is the first to look at the future of river ice on a global scale.

The research, published in the journal Nature, is the first to look at the future of river ice on a global scale.
"We used more than 400,000 satellite images taken over 34 years to measure which rivers seasonally freeze over worldwide, which is about 56 per cent of all large rivers," said Xiao Yang, a postdoctoral scholar at the University of North Carolina at Chapel Hill (UNC-Chapel) in the US.
We detected widespread declines in monthly river ice coverage. And the predicted trend of future ice loss is likely to lead to economic challenges for people and industries along these rivers, and shifting seasonal patterns in greenhouse gas emissions from the ice-affected rivers," Yang said in a statement.
The team also looked at changes to river ice cover in the past, and modelled predicted changes for the future.
Comparing river ice cover from 2008-2018 and 1984-1994, the team found a monthly global decline ranging from 0.3 to 4.3 percentage points.
The greatest declines were found in the Tibetan Plateau, eastern Europe, and Alaska.
"The observed decline in river ice is likely to continue with predicted global warming," the researchers found.
For the future, the team compared expected river ice cover through 2009-2029 and 2080-2100.
Findings showed monthly declines in the Northern Hemisphere ranging from 9-15 per cent in the winter months, and 12-68 per cent during the spring and fall.
The Rocky Mountains, northeastern US, eastern Europe, and Tibetan Plateau are expected to take the heaviest impact, the researchers said.
"Ultimately, what this study shows is the power of combining massive amounts of satellite imagery with climate models to help better project how our planet will change," said UNC-Chapel Hill Associate Professor Tamlin Pavelsky. (Source: The Business Standard)


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Global warming will lead to river ice cover decline: Study.

Why it's so hard to detect the effect of global warming on monsoon rains - Pragnya IAS Academy - News Analysis

Why it's so hard to detect the effect of global warming on monsoon rains

Even the most sophisticated climate models struggle to simulate physical processes such as convection and evaporation that drive rainfall activity.

The devastating floods in the Indian state of Kerala are a stark reminder of the vulnerability of the world’s most densely populated regions to weather and climate phenomena. In addition to the tragic loss of several hundred lives, widespread floods driven by unusually high and persistent monsoon rains have severely impacted the region’s fragile infrastructure and displaced more than a million people. Only in recent days has the Indian government been able to understand the full extent of an estimated $3 billion worth of damage.
It is now typical that the aftermath of severe weather events is marked by questions about the role played by human-induced climate change. More precisely, scientists aim to provide a timely statement about the extent to which global warming has changed the likelihood of a certain weather-related hazard. The practice of attributing an event to climate change has become a regular activity and is being tackled with a growing number of methodologies.
Improvements in the computer models used to make climate predictions means that attribution information can often be made available immediately after, and sometimes even during, the event. For instance, reports declaring this summer’s heatwave across Northern Europe to be at least twice as likely as a result of climate change were circulated while many citizens continued to experience the scorching temperatures. Being able to communicate this information while the event is still firmly in the consciousness of the general public is potentially very powerful in changing the opinions of those resistant to climate action
Effects on rainfall:
News of the worsening situation in Kerala is an opportunity to consider why understanding the effect of climate change is more difficult for some events than for others. For example, the links between global warming and temperature extremes are reasonably well understood. It should come as little surprise that a warmer world will bring more severe summer heatwaves and more frequent mild winters. When it comes to rainfall, however, things are a bit more complicated.
Unlike temperature, rainfall varies hugely in space and time.
Even the most sophisticated climate models struggle to simulate physical processes such as convection and evaporation that drive rainfall activity. On top of that, global warming is not expected to change the frequency and intensity of rainfall extremes in the same way in all parts of the world.
On a global scale, an increase in the most severe rainfall events is anticipated given the atmosphere’s capacity to hold around 7% more water per °C rise in temperature, as described by the Clausius-Clapeyron relation. But when we get to the regional scale, this relationship becomes somewhat distorted by the response of rainfall to meteorological phenomena such as tropical cyclones, thunderstorms and, in the case of the Kerala event, monsoons.
So, how should an extreme rainfall event be defined? By the amount of rain that fell or by the weather patterns that caused it?
The choice to focus solely on the rainfall itself is particularly relevant for flooding events. Though accusations of poor decision-making and mismanagement of water resources are beginning to appear in the Kerala aftermath, the floods simply would not have occurred without a significant amount of rain. Few of those suffering lost homes and livelihoods are likely to care much about where the rain came from or the intricacies of the weather conditions that led to it.
But to understand as much as possible we must consider the individual responses of weather phenomena to a changing climate. Different approaches tackle the problem in different ways – and may produce conflicting results. Even in the absence of a significant trend in the highest rainfall totals, a climate change signature may still exist in the form of rising temperatures in the oceans where the moisture that fed the rainfall originated.
Disentangling these contributory factors takes time. In comparison to droughts and heatwaves, short-term hazards such as floods do not usually give us much chance to report concrete findings while the media and general public are still engaged in the event. In-depth studies may not publish their results for many months, sometimes even years after the event in question.
Many of these issues are not exclusive to extreme rainfall. The excellent US National Academies report on Attribution of Extreme Weather Events in the Context of Climate Change describes the shortcomings in our efforts to attribute a variety of extremes. But for rainfall in particular there is a discrepancy between what we understand about the general effect of global warming and our rather lesser ability to quantify the climate change fingerprint on specific events.
While this is a cause for concern, the opportunity for improvement should be the focus of our attempts to make attribution a more effective vehicle for communicating climate risk.(Source: The Business Standard)

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Why it's so hard to detect the effect of global warming on monsoon rains

Increasing global warming leading to fish mortalities in Arabian Sea: Indo-US study - Pragnya IAS Academy - News Analysis

Increasing global warming leading to fish mortalities in Arabian Sea: Indo-US study.

Scientists say the growing abundance of green algae, Noctiluca scintillans, is a cause of concern, because they adversely affect fish, which do not thrive in such waters.

In what is set to aggravate concerns over climate change, a new joint Indo-US study has found that global warming is leading to large-scale fish kills in the Arabian Sea by fuelling the growth of harmful bioluminescent algae.
The striking green algae, Noctiluca scintillans, which is behind the scintillating phenomenon observed in oceans when they glow fluorescent blue at night, are indicators of fish mortality. Scientists highlight that their growing abundance is a cause of concern, because they adversely affect fish, which do not thrive in such waters.
“Less dense water comes to the surface because of the warming of oceans, encouraging these intense blooms, which has an adverse impact on fisheries. Currently, the western coast, Persian Gulf, and Oman are largely affected, but if it keeps on increasing, it will have drastic effects on fisheries along the Indian coast. That could be alarming,” said Dr S.C. Shenoi, director, Indian National Centre for Ocean Information Services (INCOIS).
The study jointly conducted by scientists of INCOIS, Hyderabad, and those of the National Oceanic and Atmospheric Administration (NOAA) under the US Department of Commerce, published its findings in ScienceDirect.
The new research contradicts another study, which had indicated that the massive outbreak of Noctiluca was occurring because of an increase in oxygen minimum zones.
Dr Shenoi pointed out that oxygen minimum zones are in the deeper layers of the sea and said the research team has found that there was no oxygen depleted water at the surface, where the bloom is prevalent. The dissolved oxygen in the surface water was always >70% saturated, research showed.
“A recent study had laid the blame for fish mortality on the coastal pollution caused by dumping of fertilisers and waste along the Indian coast. But this research has shown that rather than effluents or chemical pollution, it is actually global warming that is contributing to the observed abundance of Noctiluca,” said Dr Shenoi.
The researchers used sensors on board satellites to observe the distribution of these harmful algae from 2009 to 2016.
The researchers said that warming causes sea-water layers to stratify more intensely and slows upward movement of nutrients like silicate from the ocean bottom. “This discourages growth of diatoms, which need silicate and sunlight. It instead leads to flourishing of Noctiluca which preys on diatoms,” said the study.
“The present findings show no evidence that cultural eutrophication has contributed to the decadal scale shifts in plankton (algae) composition in the north- eastern Arabian Sea. Instead, the lessons that are learned here may help to forecast the effects that climate change may have in other productive oceanic ecosystems,” stated the research paper published in ScienceDirect.
Following the research, INCOIS has announced the setting up of a Marine Observation System along Indian Coast (MOSAIC) to monitor the water quality of the Indian coastal waters. (Source: Livemint)


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Increasing global warming leading to fish mortalities in Arabian Sea: Indo-US study.