Snow-vegetation-atmosphere interactions in alpine tundra

The interannual variability of snow cover in alpine areas is increasing, which may affect the tightly coupled cycles of carbon and water through snow-vegetation-atmosphere interactions across a range of spatio-temporal scales. To explore the role of snow cover for the land-atmosphere exchange of CO2 and water vapor in alpine tundra ecosystems, we combined three years (2019&ndash;2021) of continuous eddy covariance flux measurements of net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) from the Finse site in alpine Norway (1210 m a.s.l.) with a ground-based ecosystem-type classification and satellite imagery from Sentinel-2, Landsat 8, and MODIS. While the snow conditions in 2019 and 2021 can be described as site-typical, 2020 features an extreme snow accumulation associated with a strong negative phase of the Scandinavian Pattern of the synoptic atmospheric circulation during spring. This extreme snow accumulation caused a one-month delay in melt-out date, which falls on the 92nd-percentile in the distribution of yearly melt-out dates in the period 2001&ndash;2021. The melt-out dates follow a consistent fine-scale spatial relationship with ecosystem types across years. Mountain and lichen heathlands melt out more heterogeneously than fens and flood plains, while late snowbeds melt out up to one month later than the other ecosystem types. While the summertime average Normalized Difference Vegetation Index (NDVI) was reduced considerably during the extreme snow year 2020, it reached the same maximum as in the other years for all but one the ecosystem type (late snowbeds), indicating that the delayed onset of vegetation growth is compensated to the same maximum productivity. Eddy covariance estimates of NEE and ET are gap-filled separately for two wind sectors using a random forest regression model to account for complex and nonlinear ecohydrological interactions. While the two wind sectors differ markedly in vegetation composition and flux magnitudes, their flux response is controlled by the same drivers as estimated by the predictor importance of the random forest model as well as the high correlation of flux magnitudes (correlation coefficient r = 0.92 for NEE and r = 0.89 for ET) between both areas. The one-month delay of the start of the snow-free season in 2020 reduced the total annual ET by 50 % compared to 2019 and 2021, and reduced the growing season carbon assimilation to turn the ecosystem from a moderate annual carbon sink (&minus;31 to &minus;6 gC m&minus;2 yr&minus;1) to a source (34 to 20 gC m&minus;2 yr&minus;1). These results underpin the strong dependence of ecosystem structure and functioning on snow dynamics, whose anomalies can result in important ecological extreme events for alpine ecosystems.</p

Metodikk for framstilling av klimaeffekt på kort og lang sikt

CICERO Senter for klimaforskning har på oppdrag fra Miljødirektoratet utviklet og illustrert metodikk for framstilling av klimaeffekt på kort og lang sikt. Vi har vurdert klimaeffekt på to forskjellige måter, med vektfaktorer og med en veldig enkel klimamodell for å estimere temperaturbaner av utslippsbaner og utslippstiltak. Analysen bygger på tidligere arbeid CICERO har gjort for Miljødirektoratet. Mandatet CICERO fikk var analysearbeid på disse fire temaene: 1) Vurdering av behovet for å oppdatere GTP(10)-faktoren Miljødirektoratet i dag benytter. 2) Beregne norske utslipp med GTP(10), AGTP, GWP* og eventuelt andre vektfaktorer for ulike tidshorisonter. 3) Metodikk for framstilling av klimaeffekt på kort og lang sikt av ulike utslipp/utslippsreduksjoner i samme figur. 4) Metodikk for kostnadsberegninger

Metodikk for framstilling av klimaeffekt på kort og lang sikt

CICERO Senter for klimaforskning har på oppdrag fra Miljødirektoratet utviklet og illustrert metodikk for framstilling av klimaeffekt på kort og lang sikt. Vi har vurdert klimaeffekt på to forskjellige måter, med vektfaktorer og med en veldig enkel klimamodell for å estimere temperaturbaner av utslippsbaner og utslippstiltak. Analysen bygger på tidligere arbeid CICERO har gjort for Miljødirektoratet. Mandatet CICERO fikk var analysearbeid på disse fire temaene: 1) Vurdering av behovet for å oppdatere GTP(10)-faktoren Miljødirektoratet i dag benytter. 2) Beregne norske utslipp med GTP(10), AGTP, GWP* og eventuelt andre vektfaktorer for ulike tidshorisonter. 3) Metodikk for framstilling av klimaeffekt på kort og lang sikt av ulike utslipp/utslippsreduksjoner i samme figur. 4) Metodikk for kostnadsberegninger

An efficient and accurate carbon cycle model for use in simple climate models

The aim of this publication is to document a simple model of the atmospheric CO2 concentration based on exogenous input of anthropogenic emission of CO2 and taking air-sea exchange and biospheric responses into account. The approach described by Joos et al (1996) is based on the application of a mixed layer pulse response function. The advantage of using a mixed layer pulse response function instead of an atmosphere pulse response function (Siegentaler and Oeschger, 1978; Oeschger and Heimann, 1983; Meier-Reimer and Hasselmann, 1987; Sarmiento et al., 1992) is that it is then possible to represent the non-linear effects of seawater chemistry. As long as the CO2 increase in the atmosphere is below approximately 50% of the pre-industrial level, the CO2 system behaves in a linear way and it is possible to represent the effects of anthropogenic emissions on the atmospheric concentrations by an atmospheric pulse response function. For CO2 perturbations beyond this level the non-linear effects of the seawater chemistry becomes important, and it thus becomes necessary to apply a mixed layer pulse response function to obtain accurate results. The approach described in this paper includes changes in CO2 uptake and release by terrestrial vegetation by CO2 fertilization, but does not take into account possible feedback mechanisms of climate change on the carbon cycle. Possible feedbacks include changes in CO2 solubility due to sea surface temperature (SST) changes and changes in vertical mixing by reduced deep-water formation in the North Atlantic. Joos et al. (1999a) have estimated the marine part of this to be of minor importance (approximately 4%) up to 2100, increasing to about 20% in 2500. Since damage caused by climate change could imply high costs, an accurate representation of the carbon cycle is very important in models that are to be used to estimate the costs of climate and evaluate different mitigation and/or adaptation strategies (Joos et al., 1999b). The carbon cycle model described in this paper is included in a simple model for scenario studies of changes in global climate (Fuglestvedt and Berntsen, 1999)

A simple model for scenario studies of changes in global climate: Version 1.0

This paper gives a documentation of a simple climate model for studying the effects of future climate gas emissions on global mean temperature and sea level. Input to the model is global emissions of 29 gases. Atmospheric concentration of carbon dioxide (CO2) is calculated on the basis of work published by Joos et al. (1996). The parameterisation is founded on complex models for the carbon cycle where the exchange of carbon between the atmosphere, the biosphere and the oceans is considered. Future concentrations of other gases are calculated by standard equations based on emissions and chemical decay of the different gases in the atmosphere. Radiative forcing from the modelled concentrations in source gases is calculated by applying standard parameterisations published in the literature. In addition, radiative forcing is calculated for soot and sulphate aerosols (direct and indirect effects) as well as the secondary components tropospheric and stratospheric ozone and stratospheric water vapour. The estimated radiative forcing serves as input to an energy-balance-climate/upwelling-diffusion-ocean model developed by Professor Michael E. Schlesinger (Schlesinger et al., 1992). The global and hemispherical change in annual mean temperature is calculated based on the exchange of energy between the atmosphere and the oceans, and the transport of energy in the ocean. The model uses prescribed values for climate sensitivity based on GCM results. The change in sea level rise is both determined by the melting of glaciers and the thermal expansion of the ocean. The model is similar to those applied by IPCC for scenario studies (IPCC, 1996 p 316-318; IPCC, 1997; Wigley and Raper, 1992). Presently, the model serves as a useful tool in the analysis of possible global climatic changes caused by present and future greenhouse gas emissions. However, the intention is to extend the model so that regional predictions of temperature and other climate variables can be carried out

NOx emissions from aircraft: Effects of lightning and convection on changes in tropospheric ozone

A global 3-dimensional chemical tracer model (CTM) has been used to study the impact on tropospheric ozone caused by NOx emissions from today’s fleet of subsonic aircraft (0.52 Tg(N)/yr), due to uncertainties in sources of upper tropospheric NOx from lightning and deep convection. Three sets of two CTM experiments have been performed, with and without emissions from aircraft. A reference set with normal convection and 12 Tg(N)/yr from lightning, a set with reduced lightning source (5 Tg(N)/yr), and one set with reduced convective activity. A zonally homogeneous increase in upper tropospheric ozone north of 40° N, reaching 5-6 ppbv during May was found in the reference case. Reduced emissions from lighting lead to 50-70 % higher enhancement of ozone at northern mid-latitudes during summer, due to lower background concentrations of NOx and more efficient ozone production. Reduced convective mixing lead to a 40% increased enhancement in aircraft induced ozone at northern mid-latitudes and 150% in the tropics. In this case background NOx levels were higher in the upper troposphere, but the decreased ozone production efficiency was compensated by decreased downward mixing of ozone produced by emissions from aircraft

The regional temperature implications of strong air quality measures

Abstract. Anthropogenic emissions of short-lived climate forcers (SLCFs) affect both air quality and climate. How much regional temperatures are affected by ambitious SLCF emission mitigation policies is, however, still uncertain. We investigate the potential temperature implications of stringent air quality policies by applying matrices of regional temperature responses to new pathways for future anthropogenic emissions of aerosols, methane (CH4), and other short-lived gases. These measures have only a minor impact on CO2 emissions. Two main options are explored, one with climate optimal reductions (i.e., constructed to yield a maximum global cooling) and one with the maximum technically feasible reductions. The temperature response is calculated for four latitude response bands (90–28∘ S, 28∘ S–28∘ N, 28–60∘ N, and 60–90∘ N) by using existing absolute regional temperature change potential (ARTP) values for four emission regions: Europe, East Asia, shipping, and the rest of the world. By 2050, we find that global surface temperature can be reduced by -0.3±0.08 ∘C with climate-optimal mitigation of SLCFs relative to a baseline scenario and as much as −0.7 ∘C in the Arctic. Cutting CH4 and black carbon (BC) emissions contributes the most. The net global cooling could offset warming equal to approximately 15 years of current global CO2 emissions. On the other hand, mitigation of other SLCFs (e.g., SO2) leads to warming. If SLCFs are mitigated heavily, we find a net warming of about 0.1 ∘C, but when uncertainties are included a slight cooling is also possible. In the climate optimal scenario, the largest contributions to cooling come from the energy, domestic, waste, and transportation sectors. In the maximum technically feasible mitigation scenario, emission changes from the industry, energy, and shipping sectors will cause warming. Some measures, such as those in the agriculture waste burning, domestic, transport, and industry sectors, have large impacts on the Arctic, especially by cutting BC emissions in winter in areas near the Arctic

The regional temperature implications of strong air quality measures

Abstract. Anthropogenic emissions of short-lived climate forcers (SLCFs) affect both air quality and climate. How much regional temperatures are affected by ambitious SLCF emission mitigation policies is, however, still uncertain. We investigate the potential temperature implications of stringent air quality policies by applying matrices of regional temperature responses to new pathways for future anthropogenic emissions of aerosols, methane (CH4), and other short-lived gases. These measures have only a minor impact on CO2 emissions. Two main options are explored, one with climate optimal reductions (i.e., constructed to yield a maximum global cooling) and one with the maximum technically feasible reductions. The temperature response is calculated for four latitude response bands (90–28∘ S, 28∘ S–28∘ N, 28–60∘ N, and 60–90∘ N) by using existing absolute regional temperature change potential (ARTP) values for four emission regions: Europe, East Asia, shipping, and the rest of the world. By 2050, we find that global surface temperature can be reduced by -0.3±0.08 ∘C with climate-optimal mitigation of SLCFs relative to a baseline scenario and as much as −0.7 ∘C in the Arctic. Cutting CH4 and black carbon (BC) emissions contributes the most. The net global cooling could offset warming equal to approximately 15 years of current global CO2 emissions. On the other hand, mitigation of other SLCFs (e.g., SO2) leads to warming. If SLCFs are mitigated heavily, we find a net warming of about 0.1 ∘C, but when uncertainties are included a slight cooling is also possible. In the climate optimal scenario, the largest contributions to cooling come from the energy, domestic, waste, and transportation sectors. In the maximum technically feasible mitigation scenario, emission changes from the industry, energy, and shipping sectors will cause warming. Some measures, such as those in the agriculture waste burning, domestic, transport, and industry sectors, have large impacts on the Arctic, especially by cutting BC emissions in winter in areas near the Arctic