Tropical(热带的)birds deep in Brazil’s Amazon rainforest are shrinking as the world’s climate changes. Researchers studied data for 77 tropical bird species over the past 40 years and found that all of them had lost body mass, with some species losing nearly 2% of their weight per decade.

A 2019 study of birds that had crashed into buildings in Chicago, Illinois, found that they’d lost mass over a 40—year period, but those species were migratory(迁徙的). However, why the birds changed in that way was unknown. Therefore, researchers decided to examine the records of 15, 000 non-migratory birds living in a rainforest within a few hours’ drive from Manaus in Brazil.

The average temperature of the birds’ habitat is 1℃ warmer in the wet season and 1. 65℃ warmer in the dry season compared with that in 40 years ago. What’s more, 13% more rain falls in the wet season and 15% less in the dry season. The birds have lost mass more sharply following extremely dry or wet seasons. This could be a short-term response to changes in their environment, such as a lack of rainfall causing a decline in the number of insects that the birds feed on.

“Mass is a generally good indication of body condition in birds, says Vitek Jirinec at the Integral Ecology Research Center in California, who led the study. "If they’re simply not getting enough to eat, you’d expect them to lose weight.”

Birds of the same species are generally larger at higher latitudes. The leading theory is that their smaller surface — area — to — volume ratio（表面积和体积比）allows them to better conserve heat. The opposite would help smaller species in hot climates to cool and could explain why birds are getting smaller as the climate warms, says Jirinec.

The marked physical change during just four decades show why stopping destroying trees alone won’t prevent the ongoing extinctions of animal species across the world, says Camila Gomez, a scientist who studies evolutionary changes in birds. "This study also shows how human-caused changes in climate are contributing to observed population declines in tropical birds," says Gomez.

The United Nations predicts worldwide temperatures over the next five years may at times rise to more than 1. 5 degrees Centigrade above pre-industrial levels. The U. N. 's World Meteorological (气象的) Organization,WMO, said the prediction suggests continued warming could present a challenge to climate change goals set in the 2015 Paris Agreement, which seeks to limit world temperature rises through major cuts in human-caused greenhouse gases.

The WMO said there was a 20 percent chance that the yearly average temperature will rise above 1.5 Celsius higher than the pre-industrial average levels in at least one year. The report identifies 1850-1900 as the pre-industrial period. That does not mean that the average would be crossing the long-term target of 1.5 Celsius that scientists have set as the limit for avoiding catastrophic（灾难性的)climate change.

Temperatures over the last five years have been the warmest on record,the WMO reported. Temperatures over the next five years are very likely to be within the range of 0.91 to 1.59 Celsius above pre-industrial levels, it predicted. Almost all of the world, except for parts of the southern oceans, are likely to be warmer than the recent past, which is defined as 1981 to 2010. Southern Africa and Australia, where fires last year destroyed millions of hectares (公顷)，will probably be drier than usual through 2024, the report said. Africa's Sahel region is likely be wetter,while Europe should see more storms.

Maxx Dilley, the WMO's director of climate services, told the Associated Press the predictions are worrisome. "It shows how close we're getting to what the Paris Agreement is trying to prevent,”he said. Still, Dilley added that it would not be impossible for countries to reach the target set in Paris, of keeping global warming well below 2 degrees Celsius, by the end of the century. Petteri Taalas, the WMO Secretary-General,added,"While COVID-19 has caused a severe international health and economic crisis, failure to cope with climate change may threaten human well-being, ecosystems and economies for centuries.”

The gradual heating of Earth's surface, oceans and atmosphere is primarily caused by human activity. We burn fossil fuels, and pump carbon dioxide and other greenhouse gases into the atmosphere. These gases act like a greenhouse.   【小题1】

Already, the consequences of global warming are measurable and visible【小题2】Lakes around the world are warming rapidly-in some cases faster than the surrounding environment. Animals are changing migration patterns, and plants are budding their leaves earlier in the spring and dropping them later in the fall.

One of the most immediate and obvious consequences of global warming is the increase in temperatures around the world. The average global temperature has increased by 0.8℃ over the past 100 years, according to the National Oceanic and Atmospheric Administration.【小题3】That year, Earth's surface temperature was 0.99℃ warmer than the average across the entire 20th century.

【小题4】We have more unpredictable extreme weather. These extremes come in different flavors. One effect can be colder than-normal winters. Changes in climate can cause the boundary between the cold North Pole air and the warm equatorial air to migrate south.【小题5】This is why some areas can have a sudden cold snap or colder-than-normal winter, even during the long-term trend of global warming.