Over the southern hemisphere’s summer, mercifully now at an end, Australia burned under a pitiless sun. Bush fires down the continent’s eastern part consumed 46 acres of countryside, destroying homes, taking lives and driving rare animals towards extinction. To many Australians, the satellite pictures showing huge amounts of smoke drifting off to the east over the Great Barrier Reef seemed a threat to life in an age of man-made warming.

It turns out that high temperatures were doing great damage under the water as well. This month comes news that exceptionally warm seas have led the Great Barrier Reef, the world’s biggest coral system, to suffer its third mass bleaching in five years. The bush and the reef: Australians almost define themselves by these two ecosystems, which once seemed boundless.

Coral bleaching takes place when sea temperatures rise sharply, causing the coral polyps that make up reefs to spray the algae(海藻) that generate their food via photosynthesis(光合作用).Without the colour algae, coral soon dies, leaving the complex colonies a ghostly white. Reefs can recover from occasional bleachings: the fastest-growing corals regenerate in a decade or so. But mass bleachings on the Great Barrier Reef are becoming ever more frequent. And the run of recent bleachings had already killed off relatively heat-intolerant coral species. What is striking this year is that for the first time the bleaching extended to the southern part of the reef. There, closer to the pole, waters should be cooler. But not this year.

The biblical rains that put out the bush fires have also helped to lower water temperatures over the reef. The rains are proof to climate-change deniers that recent fires, droughts and floods are simply part of the natural cycle. They point with delight to the bush springing back to life. Yet while important habitats depend upon fire to regenerate, this summer’s fires, exceptionally, destroyed temperate rainforests too. Regarding the reef, the deniers play down the damage and insist on the ability of “nature to fix nature”. That is despite the accumulated effect of successive bleachings from which reef struggle to recover.

The bush fires threw the prime minister, Scott Morrison, off balance. Holidaying in Hawaii made him look out if touch, while his Liberal Party’s cosy links to oil, gas, coal and iron-ore interests came under closer inspection. Mr. Morrison’s official “representative” to the Great Barrier Reef, Warren Entsch, a Queenland politician, points out that “bleached corals are not dead corals” and predicts that many will recover. Although he admits climate change is a concern, he once complained that “forcing” youngsters to be worried about it is a form of “child abuse”. Most Australian care both about climate change and about the Great Barrier Reef—but not enough, alas, to call their government out over such ambivalence.

After about two weeks of intense negotiations in Paris, delegates from around the world reached an international agreement on Dec. 12 to address climate change. For the first time in history, 195 countries have promised to reduce greenhouse gas（GHG）emissions and to increase these reductions over time.

The agreement goes beyond requiring developed countries like the US to take actions to cut down emissions. It's a universal agreement requiring some form of action from every country, rich or poor.

The agreement sets the date for an emissions peak "as soon as possible". It would also limit warming worldwide to less than 2℃ above the levels in the 1800s. According to scientific studies 2℃ is the point at which climate change will bring destructive consequences to the planet, including rising sea levels, severe droughts, increased flooding, destructive storms, and widespread food and water shortages.

The deal also urges wealthy countries to set a non- binding goal of providing more than $100 billion（650 billion yuan）per year in public and private financing by 2020 for poorer countries to help them invest in clean energy and combat the impact of climate change.

The Paris deal asks countries to make voluntary promises based on an analysis of each country's economy, politics and technology. However, the deal also includes a series of legally binding（有约束力的）requirements. It requires countries to reconvene every five years, starting in 2020, with updated plans that would cut their further emissions. Countries will also be legally required to reconvene every five years starting in 2023 to publicly report on their progress.

The Paris deal alone won't solve global warming. Its effectiveness will depend on whether each country enacts（立法）their promise. But the deal "could be viewed as a signal to global financial and energy markets, triggering a fundamental shift away from investment in coal, oil and gas as primary energy sources like wind, solar and nuclear power", according to The New York Times.

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.S 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 1.59Celsius above pre-industrial levels, it predicted. 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.”