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There is evidence that COVID-19, the disease caused by the betacoronavirus SARS-CoV-2, is sensitive to environmental conditions. However, such conditions often correlate with demographic and socioeconomic factors at larger spatial extents, which could confound this inference. We evaluated the effect of meteorological conditions (temperature, solar radiation, air humidity and precipitation) on 292 daily records of cumulative number of confirmed COVID-19 cases across the 27 Brazilian capital cities during the 1st month of the outbreak, while controlling for an indicator of the number of tests, the number of arriving flights, population density, proportion of elderly people and average income. Apart from increasing with time, the number of confirmed cases was mainly related to the number of arriving flights and population density, increasing with both factors. However, after accounting for these effects, the disease was shown to be temperature sensitive: there were more cases in colder cities and days, and cases accumulated faster at lower temperatures. Our best estimate indicates that a 1 °C increase in temperature has been associated with a decrease in confirmed cases of 8%. The quality of the data and unknowns limit the analysis, but the study reveals an urgent need to understand more about the environmental sensitivity of the disease to predict demands on health services in different regions and seasons.

RESUMO -Foi estimada a área queimada, a biomassa vegetal total acima e abaixo do solo, a formação de carvão, a eficiência de queimada e a concentração de carbono de diferentes paisagens naturais e agroecossistemas que foram atingidos pelos incêndios ocorridos durante a passagem do "El Niño" em 1997/98 no Estado de Roraima, extremo norte da Amazônia Brasileira. O objetivo foi o de calcular a emissão bruta de gases do efeito estufa liberados por combustão das diversas classes de biomassa que compõem cada tipo fitofisionômico atingido. A área total efetivamente queimada foi estimada entre 38.144-40.678 km 2 , sendo 11.394-13.928 km 2 de florestas primárias (intactas, em pé) e, o restante, de savanas (22.583 km 2 ), campinas / campinaranas (1.388 km 2 ) e ambientes florestais já transformados como pastagens, área agrícolas e florestas secundárias (2.780 km 2 ). O total de carbono afetado pelos incêndios foi de 42,558 milhões de toneladas, sendo que 19,73 milhões foram liberados por combustão, 22,33 milhões seguiram para a classe de decomposição e 0,52 milhões foram depositados nos sistemas na forma de carvão (estoque de longo prazo). A emissão bruta de gases do efeito estufa, em milhões de toneladas do gás, considerando apenas o emitido por combustão foi de 17,3 de CO 2 , 0,21-0,35 de CH 4 , 1,99-3,68 de CO, 0,001-0,003 de N,O, 0,06-0,09 de NO x e 0,25 de hidrocarbonetos não-metânicos (HCNM). O total de carbono equivalente a CO 2 emitido por combustão, quando considerado o potencial de aquecimento global de cada gás em um horizonte de tempo de 100 anos utilizado pelo IPCC, foi de 6,1-7,0 milhões de toneladas.Palavras-chave: incêndios florestais, carbono, Amazônia, Roraima, efeito estufa, El Niño, aquecimento global. Fires in the Brazilian Amazon: Estimate of Greenhouse Gas Emissions from Burning ofABSTRACT -The area burned, total biomass above and below-ground, charcoal formation, burning efficiency and the carbon concentration were estimated for the different natural landscapes and agricultural systems that were exposed to fire during the "El Niño" of 1997-98 in the state of Roraima, in the released by combustion from the various biomass classes comprising each landscape type. The total area burned was 38,14440,678 km 2 , of which 11,394-13,928 km 2 was intact primary forest, 22,583 km 2 was savanna, 1,388 km 2 was white sand scrub formations, and 2,780 km 2 was pastures, secondary forest and agricultural plots. Total carbon affected by the fire was 42.58 x 10 6 tons (t), with 19.73 x 10 6 t being term carbon storage) formed during the bums. Gross emissions of greenhouse gases emitted by 0.09 x 10 6 t NO x and 0.25 x 10 6 t NMHC (non-methane hydrocarbons). The total emission in carbon equivalent to CO 2 emitted by combustion, based on the global warming potentials for each gas over the 100-yr horizon used by the IPCC, was 6.1-7.0 x 10 6 t C.

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We test for two critical phenomena in Amazonian ecosystems: self-organized criticality (SOC) and critical transitions. SOC is often presented in the complex systems literature as a general explanation for scale invariance in nature. In particular, this mechanism is claimed to underlie the macroscopic structure and dynamics of terrestrial ecosystems. These would be inextricably linked to the action of fire, which is conceived as an endogenous ecological process. We show that Amazonian savanna fires display the scale-invariant features characteristic of SOC but do not display SOC. The same is true in Amazonian rainforests subject to moderate drought. These findings prove that there are other causes of scale invariance in ecosystems. In contrast, we do find evidence of a critical transition to a megafire regime under extreme drought in rainforests; this phenomenon is likely to determine the time scale of a possible loss of Amazonian rainforest caused by climate change.

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