We drove north for two days, to arrive at a place that existed almost entirely for one reason: To facilitate the capture and, often, consumption of wild fish. The folks who run the facility make a living providing shelter, food, boats, fishing tackle, easy access to a fishing license, and they can be hired as guides. The whole point is to locate, capture, butcher, cook, and eat the fish. The fish themselves have little say in the matter.
And while talking to the people there we got a lot of advice as to how to find and capture the fish, and offers were made to assist with the butchering and culinary preparation of the piscine prey. After a bit of final preparation and a few final words of advice, we were ready to go fish hinting.
“Except for those, fish,” the woman we were talking to said, pointing towards a particularly long dock extending into the vast lake, one of the largest lakes in North America. “Don’t catch those fish.”
“Why?” I asked perplexed.
“We named them,” she said. “You can go down and look at them, the fish that hang out at the end of that dock. A couple of Northern Pike. Don’t catch those fish.”
“OK,” I said. And off we went in the other direction to catch some different fish. I figured there were about 200 million fish of a pound or more in size in this particular lake. We could skip the ones with names.
For many decades, probably for over a century, there has been an observable, measurable, increase in global surface temperature caused by human greenhouse gas pollution. For the first several decades, this increase is a clear trend, but a mild one, and there is a lot of up and down fluctuation, with periods of several years of decrease as well as increase. Then the upward trend becomes stronger, and some time around 1970 it becomes virtually relentless, going up a good amount every decade. But still, there are fluctuations in the curve.
What causes these fluctuations? Several things. The total amount of CO2, the main greenhouse gas causing this heating, has been going up during this period without stopping. Because CO2 added to the atmosphere stays there for a long time, so even if the amount released into the air by burning fossil fuels varies, there is always an upward trend. This causes the general increase, and it is why the increase in the last 50 years or so has been stronger; more CO2 has been released each year more recently.
There are large scale interactions between the ocean, which is also heating up, and the atmosphere and sea surface, the latter being what is measured in graphs of “surface temperature.” These fluctuations are decades long, and influence the degree to which the surface is warm vs very warm. There are shorter term ocean-air interactions such as La Nina (periods when the ocean is taking in more heat) and El Nino (periods when the ocean is pumping out more heat).
As the Arctic has warmed, it has been less icy, and other parts of the Northern Hemisphere have been less snowy, so there has been less sunlight reflected away, another source of fluctuation. Also, since we are talking about the Arctic, there are fewer measurements there so the traditional curves showing global warming have not included increased rates of warming there to the degree they should. Some of the fluctuations in the surface temperature curve are caused by this kind of bias, a shifting bias (because of relatively more warming in under-sampled areas) in the data set.
Humans and volcanoes make dust. Humans used to make a lot more dust before environmental regulation required that factories and power plants clean up their act. There are varying amounts of widespread low level volcanic activity and the occasional enormous eruption. This dust affects the surface temperature curve, and the dust varies quite a bit over time.
If the earth was simpler … a rocky surface, no ocean, no volcanoes, no vegetation (and thus no wildfires as well), but a similar atmosphere, changes in the amount of CO2 or other greenhouse gasses in the atmosphere would be reflected in changes in surface temperature much more smoothly. If that was the case, the amount of variation in energy supplied by the sun would probably be visible in the curve (that factor is so small compared to the other factors that it is very hard to see in the actual data). The curve on the simple earth would probably jiggle up and down a bit but there would be relatively smooth.
If you look at the temperature curve, you can see periods of greater or lesser upward change in temperature. You can even name them. I decided to do this. I chose common baby names, half male and half female, giving male names to the periods with slower increase, female names to the periods with faster increase. It looks like this:
In recent years, in what is at the root a corporate funded, and rather nefarious effort to delay addressing the most important existential issue of our time, climate change caused by human greenhouse gas pollution, science deniers have come up with their own name for one of the fluctuations in the ever increasing upward march of global surface temperatures. They call it “hiatus” (aka “pause”). The purpose of naming this part of the curve is to pretend that global warming is not real. It looks like this:
I am not impressed. And neither should you be. This is like those fish at the end of the dock. Except for the fish it is an affectation of a few people having fun, whereas with the science deniers it is a bought and paid for attempt to cause another hiatus, a hiatus in taking action to save our future.
There is a new study, the Nth in a spate of studies looking at the “Hiatus,” that asks experts on trends (economists, mainly) to look at the surface temperature trend as though it was something other than surface temperatures (they were told it was global agricultural production), to see if they identify the hiatus.
The study is by Lewandowsky, Risbey, and Oreskes, and is “The “Pause” in Global Warming: Turning a Routine Fluctuation Into A Problem For Science. It is here.
There has been much recent published research about a putative “pause” or “hiatus” in global warming. We show that there are frequent fluctuations in the rate of warming around a longer-term warming trend, and that there is no evidence that identifies the recent period as unique or particularly unusual. In confirmation, we show that the notion of a “pause” in warming is considered to be misleading in a blind expert test. Nonetheless, the most recent fluctuation about the longer-term trend has been regarded by many as an explanatory challenge that climate science must resolve. This departs from long-standing practice, insofar as scientists have long recognized that the climate fluctuates, that linear increases in CO2 do not produce linear trends in global warming, and that 15-year (or shorter) periods are not diagnostic of long-term trends. We suggest that the repetition of the “warming has paused” message by contrarians was adopted by the scientific community in its problem-solving and answer-seeking role and has led to undue focus on, and mislabeling of, a recent fluctuation. We present an alternative framing that could have avoided inadvertently reinforcing a misleading claim.
John Abraham, at the Guardian, has written it up.
The authors show that there is no unique pause in the data. They also discuss biases in the measurements themselves which suggested a slowing in warming that actually did not occur once the data were de-biased. Finally, they reported on recent work that displayed a common error when people compare climate models to measurements (climate models report surface air temperatures while observations use a mixture of air and sea surface temperatures). With this as a backdrop, the authors take a step back and ask some seemingly basic questions.
Speaking of John Abraham, he just sent me this new graphic based on the latest surface temperature measurements. This is a good moment to have a look at it: