Extreme climatic events, implications for projections of species distributions and ecosystem structure (by Diego Fdez-Sevilla PhD)
Heat acclimation—the subtle hormonal and metabolic changes that make it easier for the body to cope with heat—is a gradual process that occurs over a few weeks of exposure to progressively higher temperatures.
For nearly two weeks, many areas in India faced temperatures that were 5.5 degrees Celsius (10 degrees Fahrenheit) above normal. May is generally the hottest month in India, but even by local standards May 2015 was unusual. By June 4, the extreme weather had claimed the lives of more than 2,500 people, according to news reports.
It has been pointed out the deathly effect that abrupt onset of heat waves can have over human populations (e.g. in India) when people have little time to acclimate to the heat.
Similarly, heat waves and abrupt changes in temperature exert a huge amount of pressure on all other biological systems, affecting species distributions and ecosystem structure. The alteration of habitats is directly linked with potential changes in their synergistic feedbacks. Species of plants covering an area have an interconnection with atmospheric humidity and adiabatic processes throughout evapotranspiration. Different species of plants have different evapotranspiration rates and changing their location will change the stability of regional feedbacks. Also the radicular configuration of plants differ between species and with it, their interconnectivity with the retention of water in the soil, also related with evaporation processes and atmospheric circulation at tropospheric level. The type of plants covering an area is also linked with the properties of albedo as part of the microclimate of the region which would be altered by having a change or loss in plant species.
These are just some examples of how abrupt changes in temperature may affect synergistic feedbacks between species distributions, ecosystem structure and atmospheric stratification and circulation.
This post complements others published previously in this blog trying to highlight the increasing relevance of understanding connecting patterns between non-biotic and biotic systems involved in atmospheric developments. The weakening of the Polar Jet Stream (as consequence of seen reduced the thermal contrast between subtropical and polar masses of air) would potentially allow “out of season” exchanges of masses of air between both sides, triggering abrupt changes of temperature wherever they move.
The weakening of the Polar Jet Stream can be linked with the changing chemical composition of the atmosphere due to increasing CO2 concentrations. The level of graduality in the transition between seasons can be affected due to the burst of Atmospheric events. If these are strong enough to alter the stability of biological systems they well might also affect the synergistic feedbacks existent between biological productivity and the thermodynamic atmospheric behaviour.
These synergistic feedbacks seem to not be of much part of the research available in the literature. Most studies are addressing the survival of species and mechanisms of adaptation against changes in climate or atmospheric behaviour. And yet, I believe that the stability of an ecosystem, biotic and nonbiotic parts altogether, has to be considered as the result of receiving and absorbing perturbations by all sides, atmosphere, biotope and ecotope. When a region losses the capacity to absorb perturbations and regenerate itself to its previous state, the whole balance between land cover and atmospheric behaviour above it will change. And thus, the climatic parameters defining the region. Only by changing the species of vegetation covering land surfaces the albedo will change, inducing changes in convective circulation as well as the chemistry of the soil and its structure.
From regional to a global change only takes to have enough regional changes to coalescence.
Some literature published addressing changes in species distributions and ecosystem structure.
The redistribution of life on Earth has emerged as one of the most significant biological responses to anthropogenic climate warming1, 2, 3. Despite being one of the most long-standing puzzles in ecology4, we still have little understanding of how temperature sets geographic range boundaries5. Here we show that marine and terrestrial ectotherms differ in the degree to which they fill their potential latitudinal ranges, as predicted from their thermal tolerance limits. Marine ectotherms more fully occupy the extent of latitudes tolerable within their thermal tolerance limits, and are consequently predicted to expand at their poleward range boundaries and contract at their equatorward boundaries with climate warming. In contrast, terrestrial ectotherms are excluded from the warmest regions of their latitudinal range; thus, the equatorward, or ‘trailing’ range boundaries, may not shift consistently towards the poles with climate warming. Using global observations of climate-induced range shifts, we test this prediction and show that in the ocean, shifts at both range boundaries have been equally responsive, whereas on land, equatorward range boundaries have lagged in response to climate warming. These results indicate that marine species’ ranges conform more closely to their limits of thermal tolerance, and thus range shifts will be more predictable and coherent. However, on land, warmer range boundaries are not at equilibrium with heat tolerance. Understanding the relative contribution of factors other than temperature in controlling equatorward range limits is critical for predicting distribution changes, with implications for population and community viability.
Causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local, short-term biological changes. Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends across diverse species and geographic regions; however, debates within the Intergovernmental Panel on Climate Change (IPCC) reveal several definitions of a ‘systematic trend’. Here, we explore these differences, apply diverse analyses to more than 1,700 species, and show that recent biological trends match climate change predictions. Global meta-analyses documented significant range shifts averaging 6.1 km per decade towards the poles (or metres per decade upward), and significant mean advancement of spring events by 2.3 days per decade. We define a diagnostic fingerprint of temporal and spatial ‘sign-switching’ responses uniquely predicted by twentieth century climate trends. Among appropriate long-term/large-scale/multi-species data sets, this diagnostic fingerprint was found for 279 species. This suite of analyses generates ‘very high confidence’ that climate change is already affecting living systems.
Species distributions have shifted in response to global warming in all major ecosystems on the Earth. Despite cogent evidence for these changes, the underlying mechanisms are poorly understood and currently imply gradual shifts. Yet there is an increasing appreciation of the role of discrete events in driving ecological change. We show how a marine heat wave (HW) eliminated a prominent habitat-forming seaweed, Scytothalia dorycarpa, at its warm distribution limit, causing a range contraction of approximately 100 km (approx. 5% of its global distribution). Seawater temperatures during the HW exceeded the seaweed’s physiological threshold and caused extirpation of marginal populations, which are unlikely to recover owing to life-history traits and oceanographic processes. Scytothalia dorycarpa is an important canopy-forming seaweed in temperate Australia, and loss of the species at its range edge has caused structural changes at the community level and is likely to have ecosystem-level implications. We show that extreme warming events, which are increasing in magnitude and frequency, can force step-wise changes in species distributions in marine ecosystems. As such, return times of these events have major implications for projections of species distributions and ecosystem structure, which have typically been based on gradual warming trends.
Global warming has caused many species to shift their geographical range towards cooler environments [1,2]. As such, the poleward redistribution of species is emerging as a significant biological response to increased global temperatures in both marine and terrestrial ecosystems [3–5]. While range shifts have been detected across decadal time-scales, by comparing historical and contemporary data, there have been few direct observations of the processes that drive population change at the range edge. Moreover, there have been far fewer observations of climate-driven range contractions compared with expansions, and, as such, the mechanisms and velocities of change at the ‘trailing edge’ are poorly understood . These issues have major implications for understanding and predicting the dynamics of range shifts .
The current paradigm implies that species ranges change continuously with warming , yet this perception cannot be reconciled with recent observations of no [8,9] or abrupt [10,11] ecological change in response to gradual warming. Alternatively, range shifts are incremental, being driven by discrete extreme events. In nature, it is likely that species exhibit a combination of both gradual and sudden, and extensive distribution shifts in response to climate when physiological thresholds are exceeded. The distinction between gradual and abrupt range dynamics has important implications for climate change mitigation because of the implied threshold dynamics and the difficulties of predicting (as well as reversing) any undesirable changes. Event-driven changes also prevent accurate estimation of the velocity of range contractions, leading to errors in projections of future impacts. Extreme climatic events are increasing in frequency and intensity as a consequence of anthropogenic climate change [12,13]. These events are likely to have major implications for natural resources, and understanding and predicting biological responses to ‘events’, rather than to ‘trends’, have become increasingly important . Evidence for species range shifts in terrestrial ecosystems, in response to both gradual warming and discrete warming events, far exceeds evidence from marine ecosystems [15,16]. As the velocity of warming in the sea is similar to that on land  and most coastal ecosystems have warmed significantly in recent decades , it is very likely that the poleward redistribution of marine biota has been severely under-reported.
Why is it important what happens to our habitats?
In October 2014 I used the following thought to introduce my posture on climate: “The introduction of the biotic component in our planet is responsible for the active transformation suffered in the chemistry of our oceans and atmosphere and, therefore, our climate.”
Recently, a new publication has stated that “The connection between oxygen levels and climate has never been considered. It turns out that it’s an important factor over geological timescales“. I cannot believe that this phrase can represent the state of knowledge in climatic research.
Sometimes I have been writing on issues of actual relevance applying intentionally fundamental knowledge and principles. My intention is to highlight the lack of perspective from the point of view of integrating “old” settled science into the “new” uncertainty uncovered with the incorporation of new techniques and data in the state of knowledge.
Following the words from George Orwell “Sometimes the first duty of intelligent men is the restatement of the obvious.”
In a fast paced environment full of new gadgets, instruments and enormous quantities of data, we face the challenge of not forgetting what we already knew, and the applications that all this knowledge have in today’s questions.
What we consider trivial, one day, it might actually become the hidden answer everybody was looking for.
The chemistry of the Atmosphere and our Oceans is directly linked with our climate and atmospheric behaviour. The obvious is to understand that such chemistry is the result of millenniums combining forces between thermodynamic and biochemical processes. But, can the obvious get forgotten and ignored so easily? Or is it its triviality?
It is because of biological systems that Oxygen increased in the Oceans. That changed the chemistry of the oceans and reduced acidification. It is water soluble and functions as an oxidator: O2 + 2 H2O + 4 e– -> 4 OH–
It is because of biological systems dry land became covered by plants, reducing albedo and thermal contrasts as well as retaining water in the soil.
Those processes are consequence of photosynthetic reactions, being the only force in our planet moving against the natural tendency for our system to increase its entropy. The human species have met the system in an equilibrium state between both forces. That has allowed life to evolve in a single genetic configuration we call DNA. When the opposing force to entropy weakens all we get is entropy, thermodynamics and uncertainty.
I believe that we are looking too much at how climatic events might harm our ecosystems, when at the same time, we should be looking at how much, harming our ecosystems, might loosen the mechanisms controlling our climate.
Oxygen currently comprises about 21 percent of Earth’s atmosphere by volume but has varied between 10 percent and 35 percent over the past 541 million years.
In periods when oxygen levels declined, the resulting drop in atmospheric density led to increased surface evaporation, which in turn led to precipitation increases and warmer temperatures, according to University of Michigan paleoclimatologist Christopher Poulsen.
“The connection between oxygen levels and climate has never been considered. It turns out that it’s an important factor over geological timescales,” said Poulsen, a professor in the Department of Earth and Environmental Sciences. While not as critical to climate as levels of heat-trapping carbon dioxide gas, oxygen plays a key role, he said.
“Oxygen concentration can help explain features in the paleoclimate record not accounted for by variations in carbon dioxide levels, and it must considered if we are to fully understand past climates,” Poulsen said. “However, variations in oxygen levels are not an important factor in present-day climate change.”
A key part of the uncertainty in terrestrial feedbacks on climate change is related to how and to what extent nitrogen (N) availability constrains the stimulation of terrestrial productivity by elevated CO2 (eCO2), and whether or not this constraint will become stronger over time. We explored the ecosystem-scale relationship between responses of plant productivity and N acquisition to eCO2 in free-air CO2 enrichment (FACE) experiments in grassland, cropland and forest ecosystems and found that: (i) in all three ecosystem types, this relationship was positive, linear and strong (r2 = 0.68), but exhibited a negative intercept such that plant N acquisition was decreased by 10% when eCO2 caused neutral or modest changes in productivity. As the ecosystems were markedly N limited, plants with minimal productivity responses to eCO2 likely acquired less N than ambient CO2-grown counterparts because access was decreased, and not because demand was lower. (ii) Plant N concentration was lower under eCO2, and this decrease was independent of the presence or magnitude of eCO2-induced productivity enhancement, refuting the long-held hypothesis that this effect results from growth dilution. (iii) Effects of eCO2 on productivity and N acquisition did not diminish over time, while the typical eCO2-induced decrease in plant N concentration did. Our results suggest that, at the decennial timescale covered by FACE studies, N limitation of eCO2-induced terrestrial productivity enhancement is associated with negative effects of eCO2 on plant N acquisition rather than with growth dilution of plant N or processes leading to progressive N limitation.