Extreme heat often brings extreme wildfires, and this year is no exception, with unprecedented heat waves fueling enormous outbreaks of fires in the western United States and Canada, as well as across the Mediterranean and in Siberia. But paradoxically, the most intense wildfires can have the opposite effect on temperatures, cooling Earth’s surface both regionally and globally.

Thick wildfire smoke can temporarily block sunlight near the ground, causing regional temperatures to drop by several degrees. Wildfire smoke can also have global cooling effects by making clouds in the lower atmosphere more reflective or blocking sunlight in the upper atmosphere, similar to what a volcanic eruption does.

The effect is far too small to counteract human-caused global warming; researchers say it’s too early to predict what it means for the broader climate system. But with fire seasons growing more intense around the world and triggering a range of extreme fire weather in North America and elsewhere, the search for answers is growing increasingly urgent.

Smoke particles act as seeds for water vapor to form clouds that are smaller and reflect more sunlight. While smoke tends to rain out of clouds fairly quickly, the Australian bushfires raged for months, pumping more and more cloud-brightening smoke into the atmosphere. “It’s not a big effect, but when you integrate over the entire Southern Ocean, it adds up,” one of the researchers says.

While this research highlights the cooling effects of smoke in the lower atmosphere, on occasion, wildfire smoke can reach even higher altitudes into the stratosphere, the layer that starts about 10 miles up. There, it can have additional effects on the climate. Smoke reaches the stratosphere when heat from a powerful wildfire creates an updraft that combines with moisture in the atmosphere to generate towering thunderclouds.

However, scientists have only recently begun studying these effects. “We might still be in the infancy of understanding how large and how important the effects of these wildfires are,” scientists say.

Most people would say the sea is blue and green. But the people who live near the coast of Zhejiang may say it is red. It is not people who caused the colour change, but very small living thing in the sea. They are algae（藻类）and protozoa（原生动物）. They come in many different colours: red, yellow or brown. Red is the easiest of those to see, so when this happens, people call it a “red tide.”

Red tides only happen when conditions in the sea are right. In the past few years, factories and people have been putting more chemicals into the sea. These chemicals help algae and protozoa to grow very quickly. The temperature of the sea is also important. Red tides usually happen at 20 to 30 degrees Celsius（摄氏的）. Red tides often happen in dry, warm areas where there is little wind. Living things grow easily in these places. Sometimes fishermen help red tides by mistake. They put small sea animals into the water for food to help fish grow.

Those living things do more than change the colour of the water--they also put poison and mucus（黏液）into the sea. This is bad for fish. The poison is bad for their brains. And too much mucus in the sea fills up fish’s gills（鳃）, so they can’t breathe. Lots of dead fish and other sea animals are now washed up on Chinese beaches.

Red tides can be bad for people, too. The algae gets inside of fish and it smells bad. It can make your eyes water. If people eat fish with too much algae inside, they could die.

Fishermen in Zhejiang are having a hard time right now. Because of the red tide, they are selling 30% less fresh seafood than usual.

In China, red tides usually happen in May and June around places like Fujian, Guangdong and Hong Kong.

Many other countries sometimes also have red tides. But it seems that we have few ways to stop red tides. They can last as long as 16 months.

Due to climate change and changes in land use, wildfires are predicted to rise by up to 14 percent by 2030, 30 percent by 2050 and 50 percent by the end of this century, and even areas once considered safe from major fires such as the Arctic, will “very likely” experience a major increase in burning, according to a new report by the UN Environment Programme (UNEP).

The report, Spreading like Wildfire: The Rising Threat of Extraordinary Landscape Fires, says that wildfires and climate change are “mutually exacerbating”. Wildfires are made more serious by climate change through increased drought, high air temperatures, low humidity, lightning, and strong winds. Meanwhile, climate change is made worse by wildfires, mostly by damaging sensitive and carbon-rich ecosystems like rainforest.

Wildfires can threaten people’s health and lives, pollute water, destroy crops and reduce land available to grow food. Costs of rebuilding after areas are struck by wildfires can be beyond the means of low-income countries. Wildlife, as well as natural habitats, is also rarely spared. All these slow progress towards the UN Sustainable Development Goals.

While the situation “is certainly extreme, it not yet hopeless”. The publication calls on governments to adopt a new “Fire Ready Formula,” with two-thirds of spending devoted to planning, prevention, preparedness, and recovery, with one-third left for response. Currently, direct responses to wildfires typically receive over half of related expenditures (开支), while planning and prevention receive less than one percent. “We have to minimize the risk of extreme wildfires by being better prepared: invest more in fire risk reduction and change from passive response to prevention and preparedness,” said Inger Andersen, UNEP Executive Director.

Setting up data and science-based monitoring systems, strengthening regional and international cooperation, restoring ecosystems and thinning forests around areas where nature and human living spaces meet are just a few suggested examples of investments into prevention, preparedness and recovery.