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Two of the world’s most prestigious science academies say there’s clear evidence that humans are causing the climate to change.

The time for talk is over, says the US National Academy of Sciences and the Royal Society, the national science academy of the UK.

The two released a paper, Climate Change: Evidence and Causes, written and reviewed by leading experts in both countries, lays out which aspects of climate change are well understood and where there is still uncertainty and a need for more research.

Sir Paul Nurse, President of the Royal Society, said:

“We have enough evidence to warrant action being taken on climate change; it is now time for the public debate to move forward to discuss what we can do to limit the impact on our lives and those of future generations.”

NAS President Ralph J. Cicerone said:

“As two of the world’s leading scientific bodies, we feel a responsibility to evaluate and explain what is known about climate change, at least the physical side of it, to concerned citizens, educators, decision makers and leaders, and to advance public dialogue about how to respond to the threats of climate change.”

Carbon dioxide (CO2) has risen to levels not seen for at least 800,000 years, and observational records dating back to the mid-19th century show a clear, long-term warming trend.

The publication explains that measurements that distinguish between the different forms of carbon in the atmosphere provide clear evidence that the increased amount of CO2 comes primarily from the combustion of fossil fuels, and discusses why the warming that has occurred along with the increase in CO2 cannot be explained by natural causes such as variations in the Sun’s output.

Many effects of climate change have already become apparent in the observational record, but the possible extent of future impacts needs to be better understood.

For example, while average global sea levels have risen about 20 cm since 1901, and are expected to continue to rise, more research is needed to more accurately predict the size of future sea-level rise.

In addition, the chemical balance of the oceans has shifted toward a more acidic state, which makes it difficult for organisms such as corals and shellfish to form and maintain their shells.

As the oceans continue to absorb CO2, their acidity will continue to increase over the next century, along with as yet undetermined impacts on marine ecosystems and the food web.

Even if greenhouse gas emissions were to suddenly stop, it would take thousands of years for atmospheric CO2 to return to its levels before the industrial era. If emissions continue unabated, future climate changes will substantially exceed those that have occurred so far, the publication says.

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