These Are the 10 Most Important Climate Stories of 2016

This year is likely to remembered as a turning point for climate change. It’s the year the impacts of rising carbon pollution became impossible to ignore. The world is overheating and vast swaths of the planet have suffered the consequences. At the same time, it’s also a year where world leaders crafted and agreed on a number of plans to try to turn the tide of carbon pollution and move toward a clean energy future. It’s clear 2016 was a year where planetary peril and human hope stood out in stark contrast. Here are the 10 most important climate milestones of the year.

The world struck an airline carbon pollution deal

The friendly skies got slightly friendlier. Air travel counts for about 7 percent of carbon emissions globally. That number will need to come down in the coming decades, and the International Civil Aviation Organization, the world’s governing body for airlines, put a plan in place to start that transition. The plan, which was signed off on by 191 countries, is focused on letting airlines buy credits that will help fund renewable energy projects to offset airplane emissions. It isn’t a perfect solution since it doesn’t directly reduce carbon pollution from air travel, but it’s a first step for an industry that will have to find novel, carbon-free ways to produce the fuel needed to fly you home for Christmas vacation.

An extremely potent greenhouse gas is also on its way out

Hydrofluorocarbons are the chemicals in your air conditioner that help keep you cool in the summer (and the food in your refrigerator cool year round). Ironically, they’re also a greenhouse gas that’s thousands of times more potent than carbon dioxide when it comes to trapping heat in the atmosphere. Reducing them is critical to keep the planet from heating up much more and in October, international negotiators struck a deal to do phase them out. Countries still have to ratify the agreement — and it could face a major roadblock in the U.S. Senate — in order for it to take effect, but if approved, it will provide strong targets and a timetable to find replacement chemicals to keep you cool in a warming world.

July was the hottest month ever recorded. Then August tied it

The Arctic had a crazy heat wave this winter, but the planet as a whole really roasted through July and August. The summer is usually the warmest time of the year by dint of the fact that there’s more land in the northern hemisphere. But this summer was something else. July was the hottest month ever recorded, and it was followed by an August — usually a bit cooler than July — that was just as scorching. Those epically hot months helped set this year up for record heat (but more on that in a bit).

Arctic sea ice got weird. Really weird

The Arctic was probably the weirdest place on the planet this year. It had a record-low peak for sea ice in the winter and dwindled to its second-lowest extent on record. The Northwest Passage also opened in August, allowing a luxury cruise ship to pass through. Those milestones themselves are a disconcerting harbinger of a warming world, but November brought an even more bizarre event. Normally it’s a time when night blankets the region and temperatures generally plummet to allow the rapid growth of ice. But a veritable heat wave ratcheted temperatures 27°F above normal, hitting pause on ice growth and even causing ice loss for a few days. December has seen a similar warm spell that scientists have found would be virtually impossible if it wasn’t for climate change. The Arctic is the most rapidly warming region on the planet and 2016 served as a reminder that the region is being dramatically reshaped by that warming.

Divestment and clean energy investments each hit a record

Climate change is a huge, pressing economic issue as countries will have to rejigger their economies to run on renewables and not fossil fuels. Investors are attacking that switch at both ends, and 2016 stands out for the record pace at which they’re doing it. On the fossil fuel side, investors representing $5.2 trillion in assets have agreed to divest from fossil fuels. That includes massive financial firms, pension funds, cities and regional governments, and a host of wealthy individuals. Not bad for a movement that only got its start in 2011. On the flip side, a report showed that investors poured $288 billion into new renewable projects in 2015, also a record. That’s helping install 500,000 solar panels a day around the world and ensuring that 70 percent of all money invested into energy generation is going to renewables.

The Great Barrier Reef was decimated by warm waters

Coral has had a rough go of it around the world for the past three years. El Niño coupled with climate change has caused a massive coral bleaching event around the globe. Nowhere have the impacts been more stark than the Great Barrier Reef in Australia. Up to 93 percent of the reef was rocked by coral bleaching as record-warm waters essentially boiled coral to death. A third of the reef — including some of the most protected areas — are now dead. Researchers found that climate change made the record heat up to 175 times more likely, offering a glimpse into the dystopian future reefs face. A 1.5°C rise in the global average temperature would essentially mean game over for corals around the world.

The world breached the 1.5°C climate threshold

So about 1.5°C. It’s a threshold that’s crucial for low-lying island states to continue their existence (to say nothing of Miami or other coastal cities). Passing it would mean essentially issuing a death sentence for these places, corals and Arctic sea ice and other places around the world. The globe got its first glimpse of 1.5°C in February and March this year. Climate change, riding on the back of a super El Niño, helped crank the global average temperature to 1.63°C above normal in February and 1.54°C above normal in March compared to pre-industrial times. While the abnormal heat has since subsided a bit, it’s likely that 1.5°C will be breached again and again in the coming years and could become normal by 2025-30.

Carbon dioxide hit 400 ppm. Permanently

Scientists measure carbon dioxide in parts per million and in 2016, and it hit a not-so-nice round number at the Earth’s marquee carbon observatory: 400 ppm. Despite the seasonal ebb and flow, there wasn’t a single week where carbon dioxide levels dipped below 400 ppm. It’s the first time on record that’s happened. Because carbon pollution continues to rise, the world isn’t going to see carbon dioxide dip below 400 ppm again in our lifetimes (and likely a lot longer than that). Carbon dioxide also breached the 400 ppm threshold in Antarctica, the first time that’s happened in human history (and likely a lot longer). And in a report that was published this year, the World Meteorological Organization revealed that carbon dioxide passed the 400 ppm milestone globally in 2015. So yeah, 400 ppm was kind of a thing this year.

The Paris Agreement got real

The world got together to deliver the Paris Agreement in 2015, but the rubber really hit the road in 2016. Nearly 120 countries have ratified the agreement, putting it into force on Nov. 4. That includes big carbon pollution emitters like China, the U.S. and the European Union, and tiny ones like Mongolia, the Cook Islands and Sierra Leone. While there’s concern that President-elect Trump could pull the U.S. out of the agreement, signatories have stressed that they’ll go forward to meet their pledges regardless. With the rubber on the road, the next step is to get the wheels spinning.

It was the hottest year on record. Again

In case it wasn’t clear, the clearest sign of climate change is heat. And this year had lots of it. Hot Arctic, hot summer, hot water, and so it’s only fitting that the biggest climate milestone of the year (in a year that itself is a milestone) is record heat. Of course, that was the biggest story in 2014. And 2015 for that matter. This year marks the third year in a row of record-setting heat, an unprecedented run. It’s a reminder that we’ve entered a new era, where our actions have changed the world we call home. We also have the ability to decide what comes next.

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