[Vedecke klimaticke forum] Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement

dobré poledne,

včerejší nature climate change vyhodnocuje data o poklesu emisí CO2 v souvislosti s opatřeními před Covid-19. Při maximu poklesu byla změna až téměř 20% globálních emisí, což je myslím docela neuvěřitelné (asi polovina tohoto poklesu byla v důsledku snížení dopravy). Odhadovaný meziroční pokles emisí je v rozmezí 4-7% (což je přibližně rychlost potřebná pro naplnění limitu 1.5°C - 2°C):

"Here we compile government policies and activity data to estimate the decrease in CO₂ emissions during forced confinements. Daily global CO₂ emissions decreased by –17% (–11 to –25% for ±1σ) by early April 2020 compared with the mean 2019 levels, just under half from changes in surface transport. At their peak, emissions in individual countries decreased by –26% on average. The impact on 2020 annual emissions depends on the duration of the confinement, with a low estimate of –4% (–2 to –7%) if prepandemic conditions return by mid-June, and a high estimate of –7% (–3 to –13%) if some restrictions remain worldwide until the end of 2020." https://www.nature.com/articles/s41558-020-0797-x

A ještě 2 studie, které zrejmě znamenají, že uhlíkový terestrický sink bude menší, než se mohlo zdát:

Increased soil release of greenhouse gases shrinks terrestrial carbon uptake enhancement under warming

Warming‐enhanced emission of soil CH₄ and N₂O corresponds to an overall source strength of 1.19, 1.84 and 3.12 Pg CO₂‐equivalent yr^‐1 under 1 °C, 1.5 °C and 2 °C warming scenarios, respectively, interacting with soil C loss of 1.60 Pg CO₂ yr^‐1 in terms of contribution to climate change. The warming‐induced rise in soil CH₄ and N₂O emissions (1.84 Pg CO₂‐equivalent year^‐1) could reduce mitigation potential of terrestrial net ecosystem production by 8.3% (NEP, 22.25 Pg CO₂ year^‐1) under warming. https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15156

Strong overestimation of water‐use efficiency responses to rising CO2 in tree‐ring studies

Using tree‐ring isotopes analysis, we assessed the magnitude of increase in iWUE after accounting for the effects of tree size, stand age, nitrogen deposition, climate and SI. We also estimated how growth conditions have modulated tree physiological responses to rising C_a. We found that increases in tree size and stand age greatly influenced iWUE. The effect of C_a on iWUE was strongly reduced after accounting for these two variables. iWUE increased in response to C_a, mostly in trees growing on fertile stands, whereas iWUE remained almost unchanged on poor sites. Our results suggest that past studies could have overestimated the CO₂ effect on iWUE, potentially leading to biased inferences about the future net carbon balance of the boreal forest. We also observed that this CO₂ effect is weakening, which could affect the future capacity of trees to resist and recover from drought episodes.

https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15166