Biological responses to climate change have most often been noted with respect to changing seasonal behavior (phenology): when do certain plants first flower, when do birds arrive, when do amphibians or insects emerge? Another class of information comes from range-shifts, for example southern species appearing more frequently north of their range. But when ranges change, population numbers are probably changing, too — becoming more numerous in some places, less in others.
This kind of information is hard to collect, as it requires fairly detailed population data from across a species' range. Under the right conditions, it's just the sort of field work that citizen scientists can conduct. In a recent issue of Nature Climate Change, Greg Breed, Sharon Stichter, and Elizabeth Crone report on data collected by members of the Massachusetts Butterfly Club between 1992 and 2010, which tells a compelling story of climate change and its effect on butterfly distributions in central New England. Club members compiled over 19,000 observations on 100 species (86% of all species known from the state), providing evidence that species whose ranges were centered north of Boston were in significant decline, while species whose ranges were centered south of Boston were increasing in numbers. Thus, from the point of view of butterflies, the Massachusetts climate has "moved south." Some common summer butterflies are in decline, for example two species of fritillary (Speyeria), which have declined by 90% since 1992. The cause is not habitat destruction or some new disease, but climate transformation. At the same time, species associated with more southern climes have been thriving. The frosted elfin (Callophrys irus), which has been historically rare in Massachusetts, has shown a 1,000% population increase.
The researchers conclude that of the possible causes for these changes, climate change is the best candidate. It's not only that the average temperature has risen several degrees in recent decades: it's also the pattern of that warming. Climate models have long predicted that winter and nighttime would show the strongest warming trend in our latitudes, and that is what the temperature data have shown.
The butterflies agree, on the evidence of this study. There are some species that overwinter as eggs or larvae, and these species show the strongest declines in abundance. The researchers suggest that "Overwintering eggs and neonates are probably more susceptible to dehydration of summers, autumns, and winters become warmer, dryer, and with less snow cover."
These changes are happening very quickly, and at a scale that makes them hard to track and respond to (for example with conservation planning). There are data showing a similar response by a few other groups (taxa) of organisms, but much more work needs to be done. The paper shows how a large, skilled group of amateur naturalists can play an important part in Expedition Earth, helping us understand how our planet is changing before our eyes, and how rapidly.
Linking weather events to climate change is problematic. By now, most of us have heard it said that individual cold snaps in the winter don’t prove there’s no warming. At the same time though, talk about global warming skyrockets during heat waves. So, how do we make sense of the relationship of weather to climate change?
Part of the problem is the media search for concrete, simple answers to an extremely complex scientific issue, complicated by the fact that climate change deniers are willing to give concrete, simple answers, and to speak in absolutes.
In addition, the global rise in temperature means that no aspect of weather is free from the influence of global warming, so every event becomes subject to scrutiny.
An analogy with the effect of steroid use on sports achievement has been widely used in recent discussions of the weather/climate link.
Baseball is a sport that keeps track of statistics. There are huge data sets and very sophisticated ways of analyzing the performance of individual players and teams, as compared with hundreds of other players' or teams' performances, decade after decade. If a baseball player starts taking steroids, you cannot say that any one home run was due to the steroids. What you can do, is look at his record at the end of the season, compare it to the years before steroid use, and say that he would not have hit that many home runs had he not been taking them.
In the same way, while we can’t say for sure “this event would not have happened without global climate change,” what we can say is that this many events of this severity would not have occurred had the climate not been warmer. As the heat rises, it changes the odds of extreme events of many kinds. This is not an assumption or a hypothesis, it is cause and effect as dictated by known laws of physics and chemistry: A majority of weather events are connected to water. When air and water are warmer, it is because there is more energy in them, and consequently, the molecules are moving around faster. The higher speed means that, in the case of water, it is less likely to stay in liquid form. Water evaporates faster, and stays in the air longer, and so higher temperatures mean worse droughts, as the heat evaporates the water, and they also mean bigger rainstorms and snowstorms when a drop in temperature allows the water to condense and fall back to the ground.
An example of this effect on a massive scale came in 2010 when a heat wave in Russia evaporated massive amounts of water, which the jet stream then carried to Pakistan. When it came down as rain in Pakistan, the resulting floods covered an area the size of the United States eastern seaboard. In fact a newly published analysis of precipitation in the U.S. between 1948 and 2011 shows that extreme precipitation events have increased in both size and severity, and record-shattering droughts are starting to seem like an annual occurrence.
When you combine that with the heat waves we’ve been seeing, and the unprecedented weather events like the massive derecho in June of this year, we can say with a high degree of confidence, that we are seeing climate change in action.
One of the persistant problems in dealing with climate change has been public perception, and that has been mirrored in the often strange views and statements from politicians and businessmen. As such, a recent rise in public talk about climate change is a positive sign, and so we have the "public messaging edition" of the Good News Page: