By Robert A. Vella
Science is often a difficult subject for many people. It’s very technical and scientists are compelled by their profession to discuss it in terms of probabilities rather than absolutes. For folks who are not scientifically inclined, this gives the false impression of ambiguity – something we intuitive humans are psychologically adverse to. In order for us to go about our daily lives, we crave the predictability and security which comes from certainty. And, the science today that is causing the most confusion and consternation is climate change.
Right now, the northern hemisphere is experiencing a rash of extreme heat waves that is alarming even the most stubborn global warming skeptics. From Japan to the U.S. southwest and to the European Arctic, bizarre weather events are impacting people in ways which seem unprecedented in our collective memories. But, is this really a result of climate change? Let’s first examine why scientists and the media are reluctant to provide a more definitive answer.
A growing field of science is starting to emerge to help us understand the precise relationship between the slowly changing global climate and the variable weather we experience daily: extreme event attribution.
Or as Michael Wehner puts it: “probabilistic” extreme event attribution. Wehner, a senior staff scientist at the Lawrence Berkeley National Laboratory, seemed careful not to frame his field as a magic bullet for assigning undisputable blame to individual weather events. “It’s not: Climate change flooded my house,” explained Wehner. “It’s: Climate change changed the chances of flooding my house.”
To understand what extreme event attribution does, it’s helpful to think about it through a simplified analogy. There’s a bucket full of balls: Some are blue, and some are red. If we draw a blue ball, the weather will be moderate. If we draw a red ball, the weather will be extreme. Before global warming, the bucket contained almost entirely blue balls with a handful of red ones mixed in. Global warming is slowly swapping a few blue balls for red ones. If today there’s a hurricane, we know that a red ball was drawn. But we don’t know if it was one of the original red balls or one of the new ones contributed by climate change. What extreme event attribution does allow us to do is estimate how many red balls were added to the bucket.
It is a convention of the media that any article about heat waves (or forest fires, droughts or hurricanes) must be footnoted with the observation that no one weather event can be definitively attributed to climate change. That reflects both an appropriate caution on the part of scientists, and a preemptive rebuttal to climate-change deniers like Sen. James Inhofe, who a couple of years ago noticed that it was cold in February and sought to cast doubt on decades of climatology by bringing a snowball to the floor of the Senate. But that consensus is beginning to break down. The rule that where there’s smoke there’s fire, which political reporters have begun to apply metaphorically to evidence of Trump campaign collusion with Russia, should apply equally to science reporters covering actual fires.
So, while this “missing link” is attributable to the difference between studying the long-term effects of climate (i.e. climatology) and studying the short-term effects of weather (i.e. meteorology), the former has a direct correlation to the latter. Therefore, the current heat waves are indeed consistent with global warming. But, isn’t this climate change natural? No, it is definitely man-made (i.e. anthropogenic).
Global warming, also referred to as climate change, is the observed century-scale rise in the average temperature of the Earth‘s climate system and its related effects. Multiple lines of scientific evidence show that the climate system is warming. Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record, which extends back to the mid-19th century, and in paleoclimate proxy records of climate change over thousands of years. The phenomenon is sometimes called “anthropogenic global warming” or “anthropogenic climate change” in view of the dominant role of human activity as its cause.
In 2013, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded, “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.” The largest human influence has been the emission of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) in the lowest emissions scenario, and 2.6 to 4.8 °C (4.7 to 8.6 °F) in the highest emissions scenario. These findings have been recognized by the national science academies of the major industrialized nations[a] and are not disputed by any scientific body of national or international standing.
The following graph detailing the various effects of radiative forcing (i.e. the primary warming and cooling mechanisms) clearly support that conclusion:
Still, doubt lingers in the minds of many. Some have recently focused on the minutiae of scientific discussion regarding these heat waves in order to shift attention away from the larger conclusions of climate research – for example, that oceanic warming and atmospheric jet stream slowing are at least partially responsible. Factually, however, both of these factors are attributable to global warming.
As humans put ever more heat-trapping gases into the atmosphere, the Earth heats up. These are the basics of global warming. But where does the heat go? How much extra heat is there? And how accurate are our measurements? These are questions that climate scientists ask. If we can answer these questions, it will better help us prepare for a future with a very different climate. It will also better help us predict what that future climate will be.
The most important measurement of global warming is in the oceans. In fact, “global warming” is really “ocean warming.” If you are going to measure the changing climate of the oceans, you need to have many sensors spread out across the globe that take measurements from the ocean surface to the very depths of the waters. Importantly, you need to have measurements that span decades so a long-term trend can be established.
These difficulties are tackled by oceanographers, and a significant advancement was presented in a paper just published in the journal Climate Dynamics.
If you have ever looked at a weather map, you’ve a seen picture of the jet stream, that wavy west to east line linking areas experiencing relatively similar weather. In the three dimensional world, jet streams are high altitude westerly winds that occur along the boundaries between air masses of different temperatures. They are driven by the temperature gradient; in the winter, when the gradient is steepest, jet streams are strongest.
A new study provides evidence that climate change may be affecting the northern hemisphere jet stream. As a result of climate change, Arctic autumn temperatures have warmed by as much as 5 degrees Celsius (9 degrees F), reducing the temperature gradient between the Arctic and temperate latitudes. In response the jet stream appears to be moving northward and its wind speed slowing. In turn, this may be slowing the westward progression of waves in the jet stream, which cause weather variation along their westward path as they fluctuate north and south.
The slowing of the jet stream, therefore, could cause weather patterns to remain in place for longer, resulting in prolonged heat waves or cold snaps.