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Kensington (United States), May 20: The world cut its daily carbon dioxide emissions by 17% at the peak of the pandemic shutdown last month, a new study found.

But with life and heat-trapping gas levels inching back toward normal, the brief pollution break will likely be “a drop in the ocean" when it comes to climate change, scientists said.

In their study of carbon dioxide emissions during the coronavirus pandemic, an international team of scientists calculated that pollution levels are heading back up — and for the year will end up between 4% and 7% lower than 2019 levels.

That's still the biggest annual drop in carbon emissions since World War II.

It'll be 7% if the strictest lockdown rules remain all year long across much of the globe, 4% if they are lifted soon.

For a week in April, the United States cut its carbon dioxide levels by about one-third.

China, the world's biggest emitter of heat-trapping gases, sliced its carbon pollution by nearly a quarter in February, according to a study Tuesday in the journal Nature Climate Change. India and Europe cut emissions by 26% and 27% respectively.

The biggest global drop was from April 4 through 9 when the world was spewing 18.7 million tons (17 million metric tons) of carbon pollution a day less than it was doing on New Year's Day.

Such low global emission levels haven't been recorded since 2006. But if the world returns to its slowly increasing pollution levels next year, the temporary reduction amounts to ''a drop in the ocean," said study lead author Corinne LeQuere, a climate scientist at the University of East Anglia.

“It's like you have a bath filled with water and you're turning off the tap for 10 seconds," she said.

By April 30, the world carbon pollution levels had grown by 3.3 million tons (3 million metric tons) a day from its low point earlier in the month. Carbon dioxide stays in the air for about a century.

Outside experts praised the study as the most comprehensive yet, saying it shows how much effort is needed to prevent dangerous levels of further global warming.

“That underscores a simple truth: Individual behavior alone ... won't get us there,” Pennsylvania State University climate scientist Michael Mann, who wasn't part of the study, said in an email.

“We need fundamental structural change.”

If the world could keep up annual emission cuts like this without a pandemic for a couple decades, there's a decent chance Earth can avoid warming another 1.8 degrees (1 degree Celsius) of warming from now, study authors said. But getting the type of yearly cuts to reach that international goal is unlikely, they said.

If next year returns to 2019 pollution levels, it means the world has only bought about a year's delay in hitting the extra 1.8 degrees (1 degree Celsius) of warming that leaders are trying to avoid, LeQuere said. That level could still occur anywhere from 2050 to 2070, the authors said.

The study was carried out by Global Carbon Project, a consortium of international scientists that produces the authoritative annual estimate of carbon dioxide emissions. They looked at 450 databases showing daily energy use and introduced a measurement scale for pandemic-related societal “confinement” in its estimates.

Nearly half the emission reductions came from less transportation pollution, mostly involving cars and trucks, the authors said. By contrast, the study found that drastic reductions in air travel only accounted for 10% of the overall pollution drop.

In the US, the biggest pollution declines were seen in California and Washington with plunges of more than 40%.

May 30: Warning of the tightrope walk ahead as governments battle the coronavirus crisis, Nobel laureate Peter Charles Doherty has expressed concern about densely populated countries such as India relaxing lockdown norms while also describing a complete shutdown as “an economic and social impossibility”.

The Australian immunologist, who cautioned that the number of COVID-19 cases will rise in the coming days, said the earliest time frame for an effective vaccine “going into large numbers of people” is nine to 12 months.

"If all goes well with testing, we could know if some of the candidate vaccines are both safe and effective as early as September/October. Then, rolling a vaccine out will depend on the type of product and how quickly it can be made, put in vials and so forth," Doherty told PTI in an email interview from Melbourne.

The novel coronavirus, he added, does not change fast like influenza and, from what is known so far, “the same vaccine should work everywhere”.

Doherty, who is with the Department of Microbiology and Immunology at the Doherty Institute, University of Melbourne, won the Nobel Prize for Medicine in 1996 for his discovery of how the body’s immune system distinguishes virus-infected cells from normal ones.

Discussing the lockdown, he said, "If it was purely a matter of hard science, everywhere should stay locked down. But that’s pretty much an economic and social impossibility.”

The expectation, he said, is the numbers will rise and limiting spread will depend on people acting responsibly and the capacity for rapid response and extensive contact testing.

“And in a densely populated country like India I think that it will be very difficult," the scientist said.

Several countries, including India, began relaxing lockdown norms in mid-May despite the WHO’s warning about a second wave. India’s lockdown began on March 25 and has since been extended. The fourth phase ends on Sunday.

Asked whether there are any alternatives to a lockdown, the 79-year-old said, "There is no other option other than closing borders. South Korea, for example, conducted massive, intensive testing and contact tracing in a wealthy country with a very disciplined population. Otherwise, not till we have effective vaccines."

He added that he personally doesn’t see the point of closing borders for people coming in if there’s already a high incidence of disease in the community, “unless it’s to avoid the need to care for them and use scarce hospital beds".

According to Doherty, the coronavirus "is a new virus which has come straight out of nature".

“It (the virus) has moved so rapidly across the world because of people travelling on international planes as well as tourist ships," he added.

The immunologist also warned against the use of hydroxychloroquine to treat COVID-19, and said current and planned trials of the anti-malaria drug should be stopped.

“My understanding is that the use of the drug in severe disease is definitely contra-indicated, but it’s not yet clear whether, if taken under medical supervision, it could have some useful effect if taken early on, or as a preventive. Those trials just haven’t been done properly," Doherty noted.

The Indian Council of Medical Research (ICMR) has backed the use of hydroxychloroquine as a preventive against COVID-19 even after the WHO suspended clinical trials of the drug citing safety concerns.

Asked whether plasma therapy can be an effective treatment for COVID-19, Doherty said, "We lack good properly controlled trials but, especially if the plasma has been tested for antibody levels and there’s evidence of good activity, it could be helpful. If I had the disease and was offered plasma therapy I would certainly accept, but I would not take hydroxychloroquine."

Doherty is also very optimistic about herd immunity developing against the SARS-CoV-2 infection.

"We think that (herd immunity) will cut in and have an obvious effect when, say, 60 per cent of people have been infected. Best hope is to boost herd immunity with a vaccine," he stated.

Herd immunity is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through vaccination or previous infections.

The number of COVID-19 cases have crossed 5.9 million and the fatalities 3,65,000, according to the Johns Hopkins University on Saturday. 

In India, the death toll has risen to 4,971 and the number of cases to 1,73,763, according to the Union Health Ministry on Saturday.

Several states, including Bihar, Uttar Pradesh, Madhya Pradesh, Jharkhand and Chhattisgarh, have reported a rise in number since lockdown norms were relaxed in early May and migrant workers reached home.

In Uttar Pradesh, for instance, the number of infections rose from around 3,000 on May 4 to 6,532 on May 26. Similarly, Bihar’s numbers increased from around 500 to over 2,700 in the period.