An international team of scientists, led by Darrell Kaufman (former INSTAAR, Northern Arizona University) and including Gifford Miller, reconstructed past climate in the Arctic over the past 2,000 years in unprecedented detail. The team found that Arctic temperatures have reversed from a long-term cooling trend and are now the warmest they have been in at least 2,000 years, bad news for the world’s coastal cities facing rising seas in the coming decades. The new reconstruction uses numerous samples from natural archives (lake sediments, ice cores, tree rings, and others) to quantify both the cooling trend and recent warming with greater certainty than ever before.
The study also included a sophisticated 2,000 year-long computer model simulation of climate change. The long-term cooling in that computer model was mostly due to the Earth’s slow rotational wobble and resulting reduction in seasonal sunlight in the Arctic. The degree and pattern of that cooling matched that shown by the natural archives, thereby increasing confidence in the computer model's ability to predict future temperature responses.
The study suggests that greenhouse gases began “overriding” the natural cooling of Earth in the middle of the last century. It further implies that the Arctic will continue to warm in the coming decades, increasing land-based ice loss and triggering global increases in sea-level rise.
The team's study was published in Science on September 4th.