Massive damage to our ecosystems
Humans have already caused the greatest mass extinction since the dinosaurs. As humans, we think we have been protecting many of the remaining natural ecosystems from human interference. The warming of the climate will slowly but steadily cause massive damage to those remaining ecosystems. In this blog, I look at the impacts of warming on natural ecosystems by latitude and then by altitude.
In the media we see that that climate change and global warming will have an impact on polar bears in the polar regions. But is there more to it than that? Human-kind has already had a massive impact on ecosystems over the last few hundred years. What will the warming of our plant do for ecologies in the tropics and in arid regions?
Massive damage by latitude
A 2019 study1 found that if the global climate warms by 2°C by mid-century, the present climate in any location would ‘move’ about 1,000 km closer to the equator. To generate the data, the authors chose a climate scenario that is a stabilization scenario. This means that it accounts for a stabilization of warming, anticipating the development of new tools for reducing greenhouse gas emissions. This is an optimistic climate change scenario. It represents conservative changes in climate conditions that are likely to occur even if substantial climate change mitigation occurs. They found that:
- Madrid’s climate by mid-century would resemble today’s in Marrakech, Morocco
- Seattle in Washington State would move two states south to the current latitude of San Francisco, California
- London, meanwhile, would be transplanted all the way to Barcelona, and
- Stockholm to Budapest
This translates to an average ‘climate velocity’ of about 20 km per year. That is 54 metres per day, or 2.25 metres per hour. This in turn is just over half a millimetre a second, easy to see with the naked eye.
So, if you are a tree or an ecosystem, how do you keep up with that rate of change to your environment? Even if your species can reproduce and proliferate quickly what happens when you get to the edge of the island or continent?
Massive damage by elevation
Another way to think of this is by elevation or altitude.
Elizabeth Kolbert’s book “The Sixth Extinction – An Unnatural History”1 describes the greatest extinction since the disappearance of the dinosaurs. In her book, Kolbert traces the history of extinctions, and of biologists’ growing awareness since the 18th century of the current mass extinction caused by humans. While past extinctions show that some species can evolve to cope with a hotter world, that evolution will be very slow. This is what makes her engaging study so scary.
In the tropics
Kolbert tells of Miles Silman and his research of tropical forests in the Andes2. Silman and his students survey 17 plots of forest along a ridge, but each at a different elevation. Plot 1 is at 3,450 m, Plot 2 is at 3,200 m, . . . Plot 6 at 2,225 m, and so on. Each plot is a hectare in size and might have several hundred trees of greater than 100 mm diameter. Each one has been surveyed meticulously every few years since 2003 to see what impact warming would have on species diversity. The average annual temperature is 2 to 3°C higher at each successive plot. Tropical species have narrow thermal ranges. Therefore, trees that are abundant in one plot may be missing entirely from the next one down or up.
Within a decade, their work revealed that the forest was already ‘in motion’. There are various ways to calculate migration rates: for instance, by the number of trees or, alternatively, by their mass. When they grouped the trees by genus, they found that global warming was driving the average genus up the mountain at a rate of 2.5 m elevation per year. But they found that there was a big range in ‘migration’ rates between genus. Some were moving at a very rapid pace of nearly 30 m a year, while others were more or less inert.
In arid regions
Anne Kelly and Michael Goulden compared surveys of plant cover that were made in 1977 and 2006–2007 along a 2,314 m elevation gradient in at Deep Canyon in Southern California’s Santa Rosa Mountains4. Southern California’s climate warmed at the surface by half a degree Celsius, the precipitation variability increased, and the amount of snow decreased during the 30-year period preceding the second survey. They found that the average elevation of the dominant plant species rose by 65 m between the surveys, with some rising as much as 142 m. The study also confirmed that the shift cannot be attributed to changes in air pollution or fire frequency. Therefore, the shift in species distribution appears to be a consequence of changes in regional climate.
So, even if a species can migrate upslope, what happens when it gets to the top of the hill or mountain range?
An imperative to slow the rate of warming
What does this all this mean? Some species may be able to regenerate at higher elevations or latitudes and flourish. But with the very rapid warming our planet is experiencing, many will not. And when there is a loss of diversity in trees in any given plot, the smaller flora and many of the fauna that thrive in each ecosystem also decline and suffer.
We have already caused the greatest mass extinction since the dinosaurs. Climate warming will slowly but steadily cause massive damage to those natural ecosystems that we – until now – think we have been protecting from human interference.
Ref 1: Bastin, J-F., Clark, E., Elliott, T., Hart, S., van den Hoogen, J., Hordijk, I., et al., 2019, “Understanding climate change from a global analysis of city analogues”, PLoS ONE 14(7): e0217592
Ref 2: Kolbert, E., “The Sixth Extinction – An Unnatural History”, Bloomsbury
Ref 3: Feeley, K. J., Silman, M. R., 2010, “Biotic Attrition from Tropical Forests Correcting for Truncated Temperature Niches.” Global Change Biology 16 (2010): 1830-36.
Ref 4: Kelly, A.E., Goulden, M.L., 2008, “Rapid shifts in plant distribution with recent climate change”, Proceedings of the National Academy of Sciences Aug 2008, 105 (33) 11823-11826
