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Sparrows are among the species most affected by this population decline in North America for 50 years. CC BY 2.0 Alan Vernon

Two reports sound the alarm at the start of a week of mobilization around the world to save the climate. A Science article reviews the loss of 3.2 billion birds over 50 years in North America (United States, Canada). While Monday 23 September, the IPCC will present its disturbing report to the UN on the oceans and the cryosphere.

The bird population in North America has fallen by a quarter since 1970, researchers say in a study published Thursday by the journal Science . It is signed by North American researchers from Cornell University (New York), the American Bird Conservancy and the National Wildlife Research Center of Canada. This study is of unprecedented scale since it covers an entire continent over 50 years.

According to their survey, nearly 3.2 billion birds have disappeared. 12 families are particularly affected by this hecatomb: sparrows, blackbirds or goldfinches. The only good news is that raptors and wetland nesting birds are doing well. The population of geese and ducks of the continent, a time threatened, even saw its population increase thanks to protective measures.

No cause determined by the study

The study does not focus on the causes of the disappearance of birds, but their authors refer to the reading of other works that have proven the impact of the extension of agricultural land. And the use of pesticides and insecticides that affect the habitat and the food source of the birds. This observation is unfortunately not unique to North America. This same trend is observed elsewhere, especially in France where 30% of the birds of the fields disappeared between 1989 and 2017. Vincent Bretagnolle considers that there is a cause common to these different falls, the intensive agriculture:

There are the same numbers in England, it's also 60-% in 50 years and in France it's 30% in 25 years.

Vincent Bretagnolle alert on the impact of intensive agriculture towards birds 20/09/2019 - by Marie Casadebaig Play

A thunderclap hoped for

The IPCC report to be presented to policy makers on Monday, September 23, will focus on the state of the oceans and the cryosphere for the first day of the UN General Assembly in New York on climate change. For the IPCC members, reporting to the 195 member states must be like a thunderclap.

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The oceans have worked well since the middle of the 19th century, absorbing more than 90% of the additional heat generated by man-made greenhouse gases. Without them, the planet would have warmed an additional 10 ° C. But that can not last. First, low temperatures favor the dissolution of greenhouse gases in water, but the average temperature of the ocean has already increased by half a degree. In addition, the seas are becoming more and more acidic. Corals disappear and microorganisms, which fix the carbon of the air by making their shells, can not do it anymore.

Irreversible melting of ice according to IPCC

Regarding the cryosphere, the frozen part of the globe: Permafrost , the frozen land of Siberia, is melting, causing a release of methane, a greenhouse gas with a warming potential 25 times higher than CO2. As for the Arctic glaciers, their melting has become irreversible. All these changes have an impact on the climate, on fish, and 27% of the world population living on the coast is directly concerned.