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Commentary: The climate policy narrative for a dangerously warming world
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It is time to acknowledge that global average temperatures are likely to rise above the 2 °C policy target and consider how that deeply troubling prospect should affect priorities for communicating and managing the risks of a dangerously warming climate.
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Predictive traits to the rescue
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Climate change poses new challenges to the conservation of species, which at present requires data-hungry models to meaningfully anticipate future threats. Now a study suggests that species traits may offer a simpler way to help predict future extinction risks.
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A systems approach to evaluating the air quality co-benefits of US carbon policies
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Because human activities emit greenhouse gases (GHGs) and conventional air pollutants from common sources, policy designed to reduce GHGs can have co-benefits for air quality that may offset some or all of the near-term costs of GHG mitigation. We present a systems approach to quantify air quality co-benefits of US policies to reduce GHG (carbon) emissions. We assess health-related benefits from reduced ozone and particulate matter (PM2.5) by linking three advanced models, representing the full pathway from policy to pollutant damages. We also examine the sensitivity of co-benefits to key policy- relevant sources of uncertainty and variability. We find that monetized human health benefits associated with air quality improvements can offset 26–1,050% of the cost of US carbon policies. More flexible policies that minimize costs, such as cap-and-trade standards, have larger net co-benefits than policies that target specific sectors (electricity and transportation). Although air quality co-benefits can be comparable to policy costs for present-day air quality and near-term US carbon policies, potential co-benefits rapidly diminish as carbon policies become more stringent.
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Human land-use-driven reduction of forest volatiles cools global climate
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Human conversion of forest ecosystems to agriculture is a major driver of global change. Conventionally, the impacts of the historical cropland expansion on Earth’s radiation balance have been quantified through two opposing effects: the release of stored carbon to the atmosphere as CO2 (warming) versus the increase in surface albedo (cooling)1. Changing forest cover has a third effect on the global radiation balance by altering emissions of biogenic volatile organic compounds (BVOCs) that control the loadings of multiple warming and cooling climate pollutants: tropospheric ozone (O3 ), methane (CH4 ) and aerosols. Although human land cover change has dominated BVOC emission variability over the past century2–4, the net effect on global climate has not been quantified. Here, I show that the effects of the global cropland expansion between the 1850s and 2000s on BVOC emissions and atmospheric chemistry have imposed an additional net global radiative impact of −0.11 ± 0.17 W m−2 (cooling). This magnitude is comparable to that of the surface albedo and land carbon release effects. I conclude that atmospheric chemistry must be considered in climate impact assessments of anthropogenic land cover change and in forestry for climate protection strategies.
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Consequences of widespread tree mortality triggered by drought and temperature stress
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Forests provide innumerable ecological, societal and climatological benefits, yet they are vulnerable to drought and temperature extremes. Climate-driven forest die-off from drought and heat stress has occurred around the world, is expected to increase with climate change and probably has distinct consequences from those of other forest disturbances. We examine the consequences of drought- and climate-driven widespread forest loss on ecological communities, ecosystem functions, ecosystem services and land–climate interactions. Furthermore, we highlight research gaps that warrant study. As the global climate continues to warm, understanding the implications of forest loss triggered by these events will be of increasing importance.
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A drought-induced pervasive increase in tree mortality across Canada’s boreal forests
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Drought-induced tree mortality is expected to increase worldwide under projected future climate changes (1–4). The Canadian boreal forests, which occupy about 30% of the boreal forests worldwide and 77% of Canada’s total forested land, play a critical role in the albedo of Earth’s surface (5) and in its global carbon budget (6). Many of the previously reported regional-scale impacts of drought on tree mortality have affected low- and middle-latitude tropical regions (2) and the temperate forests of the western United States (3), but no study has examined high-latitude boreal regions with multiple species at a regional scale using long-term forest permanent sampling plots (7–9). Here, we estimated tree mortality in natural stands throughout Canada’s boreal forests using data from the permanent sampling plots and statistical models. We found that tree mortality rates increased by an overall average of 4.7%yr−1 from 1963 to 2008, with higher mortality rate increases in western regions than in eastern regions (about 4.9 and 1.9% yr−1 ,respectively).The water stress created by regional drought may be the dominant contributor to these widespread increases in tree mortality rates across tree species, sizes, elevations, longitudes and latitudes. Western Canada seems to have been more sensitive to drought than eastern Canada.
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An extreme climatic event alters marine ecosystem structure in a global biodiversity hotspot
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Extreme climatic events, such as heat waves, are predicted to increase in frequency and magnitude as a consequence of global warming but their ecological effects are poorly understood, particularly in marine ecosystems1–3. In early 2011, the marine ecosystems along the west coast of Australia -- a global hotspot of biodiversity and endemism 4,5 -- experienced the highest-magnitude warming event on record. Sea temperatures soared to unprecedented levels and warming anomalies of 2–4 ◦ C persisted for more than ten weeks along >2,000 km of coastline. We show that biodiversity patterns of temperate seaweeds, sessile invertebrates and demersal fish were significantly different after the warming event, which led to a reduction in the abundance of habitat-forming seaweeds and a subsequent shift in community structure towards a depauperate state and a tropicalization of fish communities. We conclude that extreme climatic events are key drivers of biodiversity patterns and that the frequency and intensity of such episodes have major implications for predictive models of species distribution and ecosystem structure, which are largely based on gradual warming trends.
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Quantifying the benefit of early climate change mitigation in avoiding biodiversity loss
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Climate change is expected to have significant influences on terrestrial biodiversity at all system levels, including species-level reductions in range size and abundance, especially amongst endemic species1–6. However, little is known about how mitigation of greenhouse gas emissions could reduce biodiversity impacts, particularly amongst common and widespread species. Our global analysis of future climatic range change of common and widespread species shows that without mitigation, 57 ± 6% of plants and 34 ± 7%of animals are likely to lose ≥50% of their present climatic range by the 2080s. With mitigation, however, losses are reduced by 60% if emissions peak in 2016 or 40% if emissions peak in 2030. Thus, our analyses indicate that without mitigation, large range contractions can be expected even amongst common and widespread species, amounting to a substantial global reduction in biodiversity and ecosystem services by the end of this century. Prompt and stringent mitigation, on the other hand, could substantially reduce range losses and buy up to four decades for climate change adaptation.
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Editorial : Half-hearted engineering
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Climate warming is not the only consequence of rising levels of atmospheric greenhouse gases. The only way to counter all effects, including those on rainfall and ocean acidity, is to remove carbon from the climate system. Arguably, some of the most immediate impacts of a warming climate will result from shifts in global rainfall patterns. The potential threats are diverse, and include water scarcity in the lush Amazonian
rainforest; increased drought in the already parched southwestern United States; rainfall replacing snow in low-latitude mountain regions; and a rise in flooding in temperate climates. Whatever the exact outcome of
these threats, the stability of the world’s economy and ecosystem both depend on maintaining precipitation patterns more or less as they are today.
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Stronger winds over a large lake in response to weakening air-to-lake temperature gradient
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The impacts of climate change on the world’s large lakes are a cause for concern1–4. For example, over the past decades, mean surface water temperatures in Lake Superior, North America, have warmed faster than air temperature during the thermally stratified summer season, because decreasing ice cover has led to increased heat input2,5. However, the effects of this change on large lakes have not been studied extensively6. Here we analyse observations from buoys and satellites as well as model reanalyses for Lake Superior, and find that increasing temperatures in both air and surface water, and a reduction in the temperature gradient between air and water are destabilizing the atmospheric surface layer above the lake. As a result, surface wind speeds above the lake are increasing by nearly 5% per decade, exceeding trends in wind speed over land. A numerical model of the lake circulation suggests that the increasing wind speeds lead to increases in current speeds, and long-term warming causes the surface mixed layer to shoal and the season of stratification to lengthen. We conclude that climate change will profoundly affect the biogeochemical cycles of large lakes, the mesoscale atmospheric circulation at lake–land boundaries and the transport of airborne pollutants in regions that are rich in lakes.
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