The extent of Arctic sea ice is an important marker for global climate change. In the last forty years it also has been unequivocally shrinking. NASA has been tracking Arctic sea ice extent at different times of the year, with the September minimum being an important point of comparison. Like any chaotic system there are going to be short term fluctuations, but the long term trend is crystal clear. Look at the graph and look at the video on the NASA site linked above – the shrinking is clear.

The first estimates for September 2017 are in and they are consistent with the overall trend. Arctic sea ice’s most recent maximum for the September minimum was in 1996 at 7.87 million square km. The minimum minimum was in 2012 at 3.62 million sq km – less than half. This year the minimum is estimated to be 4.7 million sq km, slightly more than 2016. All of the last 10 years are below the average for the previous 30 years.

This past year we had a warm winter, which led to the lowest amount of March Arctic sea ice on record, but a cool summer allowed the Arctic ice to rebound a bit.

All of this adds to the strong scientific consensus that the globe is warming and this trend is largely due to human factors (not natural cycles). But as you probably know, there is a well-financed campaign of denial, ideologically and financially motivated, to muddy the waters and create doubt and confusion about this scientific consensus. This is easy to do with complex scientific questions.

For example – what is the best time frame in which to view the changes in global average temperatures, Arctic sea ice, or some other marker? If you zoom in on the data too closely you see the year-to-year noise. If you back up too far you see natural trends that happen on the scale of tens of thousands or millions of years, and short term changes are lost. If you look at trends in the data over decades and centuries, however, then the noise flattens out and you can see what is happening over a relevant period of time. It’s easy to change your focus, however, to get the view that you ideologically desire.

You can also focus on a different subset of the data. For example, if you just look at Antarctic sea ice, it has been increasing over this same time period. But this needs to be put into context. First, Antarctica is different than the Arctic. The Arctic is all ocean, there is no land mass there. Antarctica is a continent, so it has continental ice and is surrounded by sea ice, so the dynamic is different. We need to look more thoroughly at the overall ice situation to see what is happening.

First, if you look at total sea ice at both poles, that is decreasing. The loss of Arctic sea ice is greater than the increase in Antarctic sea ice. The dynamics in the Antarctic are also different. The water there is isolated by a circumpolar current around the continent. Ice is also fed by fresh water, which freezes more easily, and wind and precipitation coming off the ice shelf.

Further, if you look at the continental ice the Antarctic glaciers are losing mass. However, there was already a general trend toward greater snow fall in the Antarctic, although that trend has slowed. It is still disputed whether the total snow and ice mass in the Antarctic is increasing or decreasing, but the trend is turning down in either case.

If we back up all the way and look at total global ice, which seems like the best measure and avoids any cherry picking, the trend is also clear. Total global ice is decreasing, including glaciers, continental ice shelves, and sea ice.

Is there room for any doubt? Sure, there is always room for doubt in science, it’s built into the process. That is another source of confusion, however. Scientists talk about our level of confidence, and the robustness of the consensus, which is at a fairly high level considering the complexity of the topic. Politicians and those advocating that we do something about climate change, however, may state things in a way that they feel captures the situation, but is not strictly scientific. For example, they may say that climate change is a fact and settled science. Deniers then exploit this to argue that those who accept climate change are trying to shut down debate and are not being scientific.

None of this touches the strong scientific consensus, however. Further, we can simultaneously accommodate the built in doubt and openness required by science and the need to make decisions based on what we do know. The level of consensus, and the level of certainty about the fact that adding large amounts of carbon to the atmosphere is driving a trend of global warming is high enough to justify taking preventive actions.

If a doctor is treating a patient and they are 95% certain they have an infection requiring an antibiotic, and two other doctors are also consulted and they agree with the recommendation, it is probably best to start antibiotics rather than watch the patient die while debating the 5% uncertainty. You have to make a risk vs benefit assessment based on the data and uncertainty that we have.

If we make a risk vs benefit assessment of anthropogenic global climate change, even acknowledging all the uncertainties, it seems obvious to me that the prudent thing to do is to take some rational steps to mitigate climate change. That does not mean ruining our economy, as deniers will claim. It could mean simply accelerating research and developing into carbon neutral energy sources, and encouraging their early adoption.

As I have argued before, burning fossil fuels has multiple costly negative effects, not just climate change, including pollution and adverse health outcomes. The finances are pretty clear at this point – money invested in non-polluting renewable sources of energy is money well spent, and it will save us much more money in the future while improving quality of life.

Renewable energy sources are the technology of the future, can lead to energy independence, reduced pollution, and improved health. Even if you don’t mention climate change, it is still advantageous to switch to renewables. That is a point worth driving home. And if we prevent a climate disaster, that’s good too.