In many ways, climate change this year was no different to all the other years since the turn of the century. Early data from the World Meteorological Organization shows global temperatures to be simmering away at 1.2° C (2.2° F) above pre-industrial levels, on track to make 2016 the hottest on record. If that phrase sounds familiar, it is because it would mean 16 of the 17 hottest years recorded have occurred since 2000, the other being 1998. But the year threw up plenty of surprises too, an Arctic heatwave, massive coral bleaching and the election of a certain unpredictable leader, just to name a few. Here's a look at the key events to shape the year in climate science, and what they might mean as we sweat into 2017 and beyond.
A warmer Arctic
Let's take it from the top, that freezing, hostile place that Santa calls home. About midway through the year, NASA scientists studying Arctic sea ice found that it was melting at a record-breaking rate, with levels declining by about 13.4 percent per decade. Its total coverage at the height of the melting season in September is now 40 percent less than in the late 1970s.
"I would say that perhaps the most spectacular sign of climate extremes this year was indeed the exceptional warmth in the Arctic – beginning with temperatures just around the freezing point in January 2016 (when normally these are between -25 and -40°C/-13 and -40° F) and the repeated warmth in the last few weeks," Martin Beniston, Director of the Institute for Environmental Sciences at the University of Geneva, tells New Atlas. "This is also linked to record low surface areas of sea ice in the Arctic Ocean recorded in September."
What normally happens is that September passes and the sea ice coverage builds again. But 2016 was different. The freakishly warm weather meant that ice coverage has remained at record low levels since late October as winter approaches (despite the best efforts of migrating birds, whose poop help keep it cool, it was revealed in November). Scientists studying this trend say that the record November and December temperatures do not occur in modeling that leaves out human-driven climate factors.
The disappearing habitat of polar bears is one well-known consequence of climate change in the Arctic, but earlier this month researchers discovered another animal that is having a hard time up top. The warmer temperatures mean more rainfall on the Norwegian archipelago of Svalbard, which freezes on top of the snow and seals reindeer food below a sheet of ice. The animals have experienced a 12 percent decrease in average body mass over 16 years as a result.
"The changes in the arctic are scary because no one knows what they portend," says Dr Tim Barnett, an emeritus research marine geophysicist at Scripps Institution of Oceanography.
So what about the other end of the globe? In November, evidence arising from the logbooks and journals of early 20th century explorers suggested that Antarctic sea ice coverage is fluctuating over decades-long cycles, rather than a steady downward trend, and therefore appears less vulnerable to climate change than the Arctic.
But nonetheless, scientists are increasingly concerned with the state of the West Antarctic ice sheet. In 2015, a nearly 225 sq mi (582 sq km) iceberg broke off the region's Pine Island Glacier. Researchers were unsure of the cause of the event until in November, some new imaging software revealed that a rift had formed at the base of the ice shelf, around 20 mi (32 km) inland.
This rift propagated upwards over two years until it burst through the ice surface and sent the iceberg on its merry way out to sea. In simple terms, the ice sheet is breaking up from the inside out. This could bring more melted ice into the ocean and flood coastlines the world over. For Dr. Virginia Burkett, who was a lead author on the Intergovernmental Panel on Climate Change's Nobel Peace Prize-winning fourth assessment report, and is now Associate Director of Climate and Land Use Change at the United States Geological Survey, 2016's climate revelations didn't come any bigger.
"The most significant science news in my mind is the new understanding we have gained on the vulnerability of the West Antarctic ice sheet," Burkett tells New Atlas. "I am a coastal ecologist and the latest observations and process-oriented studies reveal that the ice sheet may be much more vulnerable than previously thought. This has serious implications for low-lying coastal and island communities around the world."
Putting the global in global warming
Record-breaking heat wasn't the only landmark event when it comes to the climate in 2016. We also saw carbon dioxide concentrations in the atmosphere over the South Pole tip over 400 parts per million (ppm) for the first time in four million years. Experts say 350 ppm is a concentration that is safe. But we are well beyond that now, with the South Pole the final location to surpass this symbolic but dangerous threshold.
"The far Southern Hemisphere was the last place on earth where CO2 had not yet reached this mark," Pieter Tans, the lead scientist of NOAA's Global Greenhouse Gas Reference Network, said at the time. "Global CO2 levels will not return to values below 400 ppm in our lifetimes, and almost certainly for much longer."
While the greenhouse gases emitted through human activity are enough on their own, research published in early December revealed that the Earth may be about to make its contribution of its own. Scientists studying the carbon stored in the planet's soil found that as temperatures rise, it will escape into the atmosphere as a result of heightening microbial activity. So much so, that it would be the same as adding another United States to the planet's carbon footprint by mid-century.
Last year's Paris Agreement on climate action is intended to put the brakes on these trends. A total of 195 countries have signed the accord, pledging to cut greenhouse gas emissions in order to keep global temperatures from rising 2° C (3.6° F) above pre-industrial levels this century.
"The Paris accord is the first global recognition that there is a problem," says Burkett. "The treaty is weak and full of holes, but it is a start."
But only one year on the UN has declared the need to go well beyond the initial commitments. According to current projections, to keep warming below 2° C, greenhouse gas emissions in the year 2030 need to be kept to 42 gigatons. But the UN's annual Emissions Report released in November found we are currently on track for 54 to 56 gigatons, a figure that would put us on a path to temperature rises of 2.9 to 3.4° C (5.22° F to 6.12° F) by the end of the century.
The election of Donald Trump casts more uncertainty over the future of the Paris Agreement. Having previously called climate change a hoax, Trump vowed to withdraw the US from the Paris Agreement and remove restrictions on energy production, so his impending move to the Oval Office prompted us to ponder, what does all this mean for the planet?
While many of the ramifications of global warming hang in the air, some are already being felt on the ground. In June, scientists attributed a mammal's extinction to climate change for the first time. Rising sea levels in Australia's Great Barrier Reef had washed away the vegetation that serves as food for a rodent called the Bramble Cay melomy, driving the already endangered animal to extinction.
"We can't really point the finger at any other thing," Dr Luke Leung, ecologist at the University of Queensland, told us at the time. "This species has persisted very well for a very long time on such a small cay. We found evidence of tidal surge killing the plants and leading to the disappearance of this species on the island, so we are very confident that this extinction was caused by climate change."
This is a sign of things to come, according to the World Wildlife Fund, which released a report in October predicting that global wildlife populations could drop by as much as two thirds by the year 2020. Habitat loss, degradation, pollution, and invasive species are cited as a few of the reasons for this trend, along with human-induced climate change.
The deep blue (more acidic) sea
Scientists estimate around one quarter of the excess carbon dioxide we pump into the atmosphere is absorbed by the ocean. This triggers chemical reactions that increase the acidity of the seawater. The effects of this are varied, but in 2016 we saw this play out in a few very dangerous ways.
More acidic seawater dissolves the calcium carbonates that serve as the building blocks for coral reefs. Combine this with warming oceans, which cause stressed algae to be expelled from the tissue of coral that in turn withers and dies, and you have a recipe for severe, unprecedented damage to the world's reefs. Australia's Great Barrier Reef suffered through the worst coral bleaching event in its history in 2016, with around two thirds of the coral in the reef's northern section dying as a result.
This year we also learnt how more acidic oceans might affect the behavior of sea life in more subtle ways. A study in July suggested that higher acidity in the ocean could weaken the defenses of black turban snails, causing them to move more slowly and therefore be less able to escape the predatory clutches of ochre sea stars. Another study in October revealed that more acidic waters can throw the survival instincts of fish out of whack, even sometimes sending them swimming towards predators.
While environmental devastation is the growing concern, 2016 brought some positive climate stories, too. Geoengineering has its skeptics (and outright critics), but plenty of scientists are exploring how we might manipulate the environment to soften the blow of a changing climate. Earlier this month, scientists overcame one of the roadblocks facing the idea of solar-geoengineering, discovering an aerosol that could be introduced into the atmosphere to bounce heat back out into space, without degrading the ozone layer in the way previously suggested approaches would do.
Another branch of geoengineering is carbon dioxide capture, and back in June scientists made a significant breakthrough in this area. Typically, carbon capture involves stowing away captured carbon in underground reservoirs, where it converts into solid carbonate minerals over hundreds or thousands of years, the kind of timeframe that brings plenty of opportunities for leaks.
But scientists found that basaltic rocks in Iceland's geothermal fields could seriously fast-track this process. They came up with a process that involves turning carbon dioxide into carbonated water, pumping it into underground wells where elements like calcium, magnesium and iron turn more than 95 percent of the CO2 into solid minerals within just two years. Another promising advance in carbon capture came in September, when researchers developed special ultra-thin bubbles called Menzymes that they claim can offer a low-cost and more efficient way to capture and dissolve C02.
And while storing captured carbon away in underground reservoirs is one way of dealing with it, there are plenty of technologies under development that would put it to use in more productive ways.
One line of thinking is that it could be turned into concrete. In April, scientists at the University of California made some real progress towards this goal with something they dubbed Co2ncrete, which is the product of a manufacturing method that takes the carbon dioxide emitted during the calcination of limestone and turns it into concrete using 3D printing. The team used the technique to produce tiny Co2ncrete cones and, having described their success as proof of concept, are now setting their sights on scaling things up to commercial volumes.
Another way C02 could be put to use is in new forms of fuel, and 2016 brought a few exciting advances in this area. In February, scientists at the University of Texas at Arlington demonstrated a one-step conversion process whereby they could turn carbon dioxide and water straight into a simple and inexpensive liquid hydrocarbon fuel. And just this month, scientists found that nitrogen-doped graphene quantum dots can work as a catalyst in an electrochemical reaction that turns carbon dioxide into ethylene and ethanol.
Also on the positive side of the climate science ledger in 2016 were revelations involving the atmosphere, including research in September that found atmospheric acidity is almost back to pre-industrial levels, and that 30 years after the world banned the use of CFCs, the hole in the ozone layer is on the path to recovery. There was also research from scientists studying NASA satellite data that revealed increased C02 levels are boosting the Earth's vegetation, and in an interesting example of how a changing climate could turn the world on its head, another study found a predicted boost in rainfall in the Blue Nile Basin could turn Ethiopia into a food-exporting nation.
Brand new tools
As the planet is heating up, so too are the efforts to learn more about this phenomenon, and 2016 gave us some new ways to fill in the blanks. Ice can be a valuable recorder of the past, and as it disappears so too do the secrets that it holds. The Protecting Ice Memory project is working to preserve these scientific samples by pulling 130-meter-long (427-ft) ice cores from the Mont Blanc Massif in the French Alps and stowing them away. In July the frosty library got its first deposit.
In a similar vein, a historic agreement was reached between countries to declare Antarctica's Ross Sea an official marine Protected Area, the largest such reserve in the world. Home to more than 10,000 species including orcas, minke whales and penguins, scientific data in the Ross Sea goes back 170 years, so it has been, and will now continue to be, an invaluable resource for studying the impacts of climate change on these ecosystems.
As much as 90 percent of the warmth we are adding to the Earth system is absorbed by the ocean, but tracking temperature changes in the sea is a bit of an inexact science relying on ship measurements and a network of drifting floats. Earlier this month, NASA scientists presented a proof-of-concept study describing a technique that tracks deviations in the Earth's magnetic field as it passes through the ocean to detect temperature changes in this huge environment.
Renewables and a brighter outlook
The year also marked a notable shift in the mentality toward renewable energy. In recent months, France, the UK and the Netherlands pledged to shut down coal-powered plants by 2023, 2025 and 2030, respectively. These follow moves by smaller European nations like Belgium, Cyprus and Malta to phase out the fossil fuel and signal real willingness to adhere to their Paris Agreement commitments.
In October, the International Energy Agency released a report revealing that renewables have now overtaken coal as the world's largest source of installed power capacity. Half a million solar panels were installed around the world every day in 2015, along with two wind turbines in China every hour.
The agency projects that global power capacity from renewables will exceed 7,600 TWh (terawatt hours) by 2021, which is equal to the combined electricity generation of the US and Europe today. And it doesn't hurt that big names like Google are choosing to get in on the action either – earlier this month the company pledged to run all of its global operations on renewable energy from next year onward.
2017 and beyond
So it feels like the wheels are really beginning to turn on a shift toward renewable energy, but even if we forge ahead at breakneck speed it will take a long time to impact the warming trend. 2017 is sure to bring its share of surprises, though there is one environmental impact that wouldn't catch us off guard: if the coming year is again warmer than the last.