Extreme and unpredictable weather is expected only to get worse as the planet's major fresh water ice sheets melt, New Zealand-led research has found.
Last week it was colder in Chicago than at the North Pole, while wildfires raged in Australia as temperatures in Adelaide hit 47C.
Research published today in the journal Nature found such variable weather could increase due to the combined melting of the Greenland and Antarctic ice sheets.
The researchers said there could be "dangerous consequences" and called for an urgent review of global government policy.
Lead researcher Associate Professor Nick Golledge, of Victoria University of Wellington's Antarctic Research Centre, said despite the recent cold snap in the United States, overall temperatures were warming and under current policy settings the Earth's temperature would increase by 3 to 4 degrees by 2100.
"With this level of warming, a significant amount of melt water from the Greenland and Antarctic ice sheets will enter Earth's oceans," Golledge said.
"According to our models, this melt water will cause significant disruption to ocean currents and change climate around the world."
The researchers - including scientists at GNS Science, and from Canada, the United States, United Kingdom and Germany - used satellite measurements of recent ice mass changes and found that within a few decades, increasing meltwater would substantially slow ocean circulation in the Atlantic.
In the south they predicted Antarctic meltwater would form a "freshwater lens" on the surface, allowing rising warmer water to spread out and potentially cause further melting of Antarctic ice underwater.
They predicted a level of melt from freshwater of 25cm by 2100. While this was a very small amount in comparison to the ocean, which averaged about 2 to 3km deep, it had a big impact on the "delicate" ocean.
"The way fresh and salt water act in the ocean is very delicately balanced, and even though this is a relatively small amount going in it produces a big knock," Golledge said.
"When you mix cold fresh water in the ocean it changes the way the water mixes as they have different densities, which changes the way heat is transported around the globe."
Model predictions showed these changes would lead to more extreme weather events and greater year-to-year variation in temperature in some parts of the world.
In the North Atlantic Ocean the influx of meltwater would significantly weaken deep Atlantic circulation, which affected coastal ocean currents such as the Gulf Stream.
This would lead to warmer air temperatures in Central America, Eastern Canada, and the high Arctic, but reduced warming over northwestern Europe on the other side of the Atlantic.
More heat would be trapped in the Gulf of Mexico, meaning the frequency and intensity of hurricanes there could increase.
"We know that anything that increases heat is going to make it easier for these extreme events to happen, more often and with more intensity," Golledge said.
While their research did not include any specific findings for New Zealand, it would be impacted by the unpredictability of the weather.
"We will start to see more of this recent extreme weather, both hot and cold and with bigger differences year to year.
"We can adapt to steady changes, but that unpredictability could have incredibly disruptive effects for agriculture, infrastructure, and human life itself."
These extreme weather models were not accounted for in current global climate policies, Golledge said.
"Mitigation, reducing emissions, is still the priority.
"We want to get that down as fast we can, and New Zealand is making a great effort, with the Zero Carbon Bill and attempts to find a cross-party solution—but globally policy is lagging far behind the science.
"We will also have to talk about adaptation, things like planning and insurance. The sooner we do something the cheaper it will be."
The study was the first to use highly detailed models of both the Antarctic and Greenland ice sheets, combined with observations of recent ice sheet changes from satellites, which created more reliable and accurate predictions than achieved previously.
"Using the satellite data gives us confidence that the models are performing reliably, and the amounts of ice sheet melt we predict for the future are justified," Golledge said.
Co-author Liz Keller from GNS Science said their experiments showed sea level rise from ice sheet melt would continue even if the Earth's climate was stabilised.
"But they also show that if we drastically reduce emissions we can limit future impacts."