Friday, 7 August 2020

‘Negligible’ long-term impacts on climate from COVID-19 restrictions

Nature Climate Change
Empty streets during the Covid shutdown in Zaragoza City, Spain, Mar. 2020.
A Wikimedia photo.

The decline in greenhouse-gas emissions and air pollutants, as a result of policies to prevent the spread of COVID-19, will have a negligible impact on long-term warming and may lead to cooling of just 0.005–0.01 °C by 2030, suggests a paper in Nature Climate Change. However, the findings also suggest that if a ‘green recovery’ is pursued, warming could possibly be kept within the 1.5 °C limit above pre-industrial levels by 2050.

The enforcement of policies to limit the spread of COVID-19 has had a significant impact on travel and work. This lack of mobility has led to substantial declines in greenhouse-gas emissions and air pollutants. Previous research has examined the immediate impacts of COVID-19 policies on emissions; however, the long-term impacts of these policies are not well understood.

Piers Forster and colleagues analysed mobility data from 123 countries to estimate emission changes due to the COVID-19 restrictions from February to June 2020. Their analysis suggests that the reductions in emissions are likely to have peaked in April 2020. The authors suggest that nitrogen oxides (NOx) declined by 30% in April, which contributed to short-term cooling. However, this was offset by a 20% decline in sulfur dioxide (SO2), which weakened the aerosol cooling affect and contributed to short-term warming. They use these estimates to project future changes and compare them to a baseline scenario of current national policies. They found that these short-term effects end by 2025, leaving a longer term slight cooling of 0.01 °C from reduced atmospheric concentrations of carbon dioxide compared to concentrations under baseline policies.

To assess the longer-term impacts, the authors modelled four recovery scenarios, including a fossil fuel-based recovery and green stimulus packages. They suggest that the different scenarios have a minimal impact on the 2020–2030 climate response, but that differences emerge after 2030. They find that the two-year ‘blip pathway’, where the economic recovery maintains current investment levels, and a recovery with fossil fuel stimulus are likely to result in warming of over 1.5 °C [NOT: 2 °C] by 2050. Conversely, choosing a strong green recovery that includes low-carbon energy supply as well as energy efficiency and does not support bailouts for fossil firms could limit warming by 0.3 °C and keep warming within 1.5 °C above pre-industrial levels.

The authors highlight that economic recovery choices will affect the warming trajectory by the mid-century and argue that a green recovery is important for ensuring the goals of the Paris Agreement are met.

Thursday, 6 August 2020

Climate change: Frequency of extreme droughts across Europe predicted to rise

Nature Research
Photo "drought" by bartoszjanusz is licensed under CC0 1.0

The frequency of record-breaking two-year droughts, such as the 2018–2019 Central European drought, is expected to rise by the end of the century if projected greenhouse gas emissions aren't reduced, according to a study published in Scientific Reports.

Wednesday, 5 August 2020

Measuring ecosystem disruption caused by marine heatwaves


Above, healthy bull kelp.
Below, bull kelp degraded by
a marine heatwave. DeWikiMan
Marine heatwaves can displace thermal habitats by tens to thousands of kilometres, reports a study in Nature this week. This displacement represents the distance that an organism would have to travel to escape potentially stressful temperatures. The findings open new avenues of research to understand the potential impacts of anomalously warm ocean temperatures on marine species.

Marine heatwaves are distinct periods of unusually warm ocean temperatures that can cause dramatic changes to ocean ecosystems, as inhabitants find themselves in waters that are warmer than they are accustomed to. Much of the research into these events focuses on the local impact to species such as corals, but does not take into account mobile organisms (fish, for example) that can travel to find their preferred conditions.

To understand how species may have to redistribute under marine heatwave conditions, Michael Jacox and colleagues analyse thermal displacements associated with marine heat waves using data from 1982 to 2019. They calculate the minimum distance that a species would have to travel away from a marine heatwave to reach a habitat at their preferred temperature. This displacement varied substantially: in the tropics, where temperature gradients are small, the thermal displacement could exceed 2,000 km; in regions with sharp gradients, such as western boundary currents, displacement might be only a few tens of kilometres.

The authors note that the short-term displacement of thermal habitats is comparable to shifts associated with long-term warming trends, and may have the potential to drive rapid redistributions of marine species.

Zoonotic disease risk linked to human land use management

Cattle in the Amazon. An Adobe photo.
Human-managed ecosystems harbour more hosts of zoonotic disease than undisturbed habitats, a Nature study reveals. The research highlights the need for enhanced surveillance of agricultural, pastoral and urbanizing ecosystems, and to consider the disease-related health costs associated with land use and conservation planning.

Zoonotic diseases, such as Ebola, Lassa fever and Lyme disease, are caused by pathogens that spread from animals to people. It is widely accepted that land use change — for example, the conversion of natural habitats to agricultural land or cities — influences the risk and emergence of zoonotic diseases in humans, but whether this is underpinned by predictable ecological changes has been unclear.

Kate Jones and colleagues analysed 6,801 ecological systems and 376 host species worldwide to show that land use has global and systematic effects on local zoonotic host communities. There are more species and greater numbers of known zoonotic hosts in human-managed ecosystems than in nearby undisturbed habitats.

The effect is strongest for rodent, bat and passerine bird species, which may help to explain their prevalence as zoonotic disease hosts. As the world continues to deal with the current zoonotic COVID-19 pandemic, the authors caution that global land use change is creating increasing opportunities for contact between people and potential hosts of human disease.

Friday, 31 July 2020

Canadian ice caps disappear, confirming 2017 scientific prediction

The white patch in the lower left and dark spot in the upper right were all that remained of two, once-mighty glaciers in the region in 2016. Now, they're gone. A NASA photo.

The St. Patrick Bay ice caps on the Hazen Plateau of northeastern Ellesmere Island in Nunavut, Canada, have disappeared, according to NASA satellite imagery. Story here.

Thumbs-up for Alaskan mine draws fire

Science Magazine - Edited by Jeffrey Brainard
The area of the mine in question. Photo by Erin McKittrick
A company seeking to build a controversial gold and copper mine in Alaska won a major victory on 24 July when the U.S. Army Corps of Engineers issued an environmental analysis saying the mine wouldn’t endanger the world’s most productive sockeye salmon fishery. The decision clears the way for the Corps to issue permits needed by promoters of the Pebble Mine, located at the headwaters of two major watersheds that form part of the Bristol Bay salmon runs, just north of the Aleutian Islands.

Environmental and Native Alaskan groups and some salmon scientists blasted the new study, saying it understated risks by focusing on the mine’s small, initial footprint over 20 years of mining rather than its potential impacts if it expands to become one of the world’s largest gold and copper mines, as its promoters hope. Mine backers have said such an expansion would get a closer environmental review later if they pursue it. Scientists have raised concerns that even the smaller mine could have wide impacts, because the resilience of the salmon runs hinges on access to a wide variety of spawning habitats. Environmental groups have vowed to file lawsuits to block the project.

The second-largest ice sheet in the Arctic - Canada's Milne sheet, has collapsed.

This animation shows the sheet rapidly receding, losing almost half its mass.