Klimarealisterne slår til igen med ubalanceret omtale af greening

Overall, Nemani sees a positive message in the new findings. "Once people realize there's a problem, they tend to fix it," he said. "In the 70s and 80s in India and China, the situation around vegetation loss wasn't good; in the 90s, people realized it; and today things have improved. Humans are incredibly resilient. That's what we see in the satellite data.

Scientists say that global greening since the early 1980s may have reduced global warming by as much as 0.2° to 0.25° Celsius (0.36° to 0.45° Fahrenheit). In other words, the world would be even warmer than it is if not for the surge in plant growth.

Climate change-led increases in local and global temperatures pose a significant threat to plant growth and crop production (Priya et al., 2019). The Intergovernmental Panel on Climate Change reported that if current rates of global warming continue, global temperatures will continue to increase by a further 1.5 °C between 2030 and 2052 (Intergovernmental Panel on Climate Change, 2018). Heat stress can impair all stages of plant growth from germination to reproduction, limiting the productivity of major staple food crops (Hussain et al., 2019). For example, heat stress has a negative impact on wheat yields. A 4–6% reduction in average global yields of wheat is predicted for each 1 °C increase in global mean temperature (Asseng et al., 2015). Current concepts concerning heat stress effects on source–sink relationships and metabolome dynamics in wheat is competently reviewed by Abdelrahman et al. (2020), who place emphasis on the temperature susceptibility of the reproductive and grain-filling stages, and discuss the selection and development of germplasm that can maintain high yields under heat stress. The plant reproductive organs and processes leading to seed set are extremely vulnerable to increasing temperatures. Our current knowledge and understanding of the molecular mechanisms that contribute to this temperature sensitivity are ably discussed by Lohani et al. (2020), who summarize the regulation of male and female reproductive organ development and fertilization, together with heat-induced abnormalities at flowering. This review highlights the high-temperatur

China is the largest wheat-producing country in the world. Wheat is one of the two major staple cereals consumed in the country and about 60% of Chinese population eats the grain daily. To safeguard the production of this important crop, about 85% of wheat areas in the country are under irrigation or high rainfall conditions. However, wheat production in the future will be challenged by the increasing occurrence and magnitude of adverse and extreme weather events. In this paper, we present an analysis that combines outputs from a wide range of General Circulation Models (GCMs) with observational data to produce more detailed projections of local climate suitable for assessing the impact of increasing heat stress events on wheat yield. We run the assessment at 36 representative sites in China using the crop growth model CSM-CropSim Wheat of DSSAT 4.5. The simulations based on historical data show that this model is suitable for quantifying yield damages caused by heat stress. In comparison with the observations of baseline 1996–2005, our simulations for the future indicate that by 2100 the projected increases in heat stress would lead to an ensemble-mean yield reduction of −7.1% (with a probability of 80%) and −17.5% (with a probability of 96%) for winter wheat and spring wheat, respectively, under the irrigated condition. Although such losses can be fully compensated by CO2 fertilization effect as parameterized in DSSAT 4.5, a great caution is needed in interpreting this fertilization effect because existing crop dynamic models are unable to incorporate the effect of CO2 acclimation (the growth-enhancing effect decreases over time) and other offsetting forces.

Extreme heat stress during the crop reproductive period can be critical for crop productivity. Projected changes in the frequency and severity of extreme climatic events are expected to negatively impact crop yields and global food production. This study applies the global crop model PEGASUS to quantify, for the first time at the global scale, impacts of extreme heat stress on maize, spring wheat and soybean yields resulting from 72 climate change scenarios for the 21st century. Our results project maize to face progressively worse impacts under a range of RCPs but spring wheat and soybean to improve globally through to the 2080s due to CO2 fertilization effects, even though parts of the tropic and sub-tropic regions could face substantial yield declines. We find extreme heat stress at anthesis (HSA) by the 2080s (relative to the 1980s) under RCP 8.5, taking into account CO2 fertilization effects, could double global losses of maize yield (ΔY = −12.8 ± 6.7% versus − 7.0 ± 5.3% without HSA), reduce projected gains in spring wheat yield by half (ΔY = 34.3 ± 13.5% versus 72.0 ± 10.9% without HSA) and in soybean yield by a quarter (ΔY = 15.3 ± 26.5% versus 20.4 ± 22.1% without HSA). The range reflects uncertainty due to differences between climate model scenarios; soybean exhibits both positive and negative impacts, maize is generally negative and spring wheat generally positive. Furthermore, when assuming CO2 fertilization effects to be negligible, we observe drastic climate mitigation policy as in RCP 2.6 could avoid more than 80% of the global average yield losses otherwise expected by the 2080s under RCP 8.5. We show large disparities in climate impacts across regions and find extreme heat stress adversely affects major producing regions and lower income countries.

The effects of heat stress are spatially heterogeneous owing to local variations in climate response, population density, and social conditions. Using global climate and impact models from the Inter-Sectoral Impact Model Intercomparison Project, our analysis shows that the frequency and intensity of heat events increase, especially in tropical regions (geographic perspective) and developing countries (national perspective), even with global warming held to the 1.5 °C target. An additional 0.5 °C increase to the 2 °C warming target leads to >15% of global land area becoming exposed to levels of heat stress that affect human health; almost all countries in Europe will be subject to increased fire danger, with the duration of the fire season lasting 3.3 days longer; 106 countries are projected to experience an increase in the wheat production-damage index. Globally, about 38%, 50%, 46%, 36%, and 48% of the increases in exposure to health threats, wildfire, crop heat stress for soybeans, wheat, and maize could be avoided by constraining global warming to 1.5 °C rather than 2 °C. With high emissions, these impacts will continue to intensify over time, extending to almost all countries by the end of the 21st century: >95% of countries will face exposure to health-related heat stress, with India and Brazil ranked highest for integrated heat-stress exposure. The magnitude of the changes in fire season length and wildfire frequency are projected to increase substantially over 74% global land, with particularly strong effects in the United States, Canada, Brazil, China, Australia, and Russia. Our study should help facilitate climate policies that account for international variations in the heat-related threats posed by climate change.

Highlights

We assessed the influences of 1.5 °C and 2.0 °C warmings on the multiple sectors.

0.5 °C less warming would help avoid ~38% of the health-related heat exposure.

Forudsætningen for at kunne begrænse klimaskader er, at man tilstrækkelig tidligt får en vurdering de forventede klimaskader. Når skaderne er der er det forsent.

0.5 °C less warming would help avoid ~50% of the exposure to wildfire.


0.5 °C less warming would help avoid ~48% of the maize-related heat exposure.

Developing countries are likely to experience greater exposure to heat extremes.

Jørgen Petersen skrev:
En temperaturstigning på 3 - 4 grader i dette århundrede er fuldstændig urealistisk. Det kolde havvand vil uden tvivl holde temperaturen nede. Der skal således 3.000 gange så megen energi til at opvarme en liter vand som der skal til at opvarme en liter luft. Her ud over skal vi huske at ca. 70% at overfladen på denne klode dækket af vand.

There is a kernel of truth in this argument, experts say, based on what scientists call the CO2 fertilization effect. "CO2 is essential for photosynthesis," says Richard Norby, a corporate research fellow in the Environmental Sciences Division and Climate Change Science Institute of Oak Ridge National Laboratory. "If you isolate a leaf [in a laboratory] and you increase the level of CO2, photosynthesis will increase. That's well established." But Norby notes the results scientists produce in labs are generally not what happens in the vastly more complex world outside; many other factors are involved in plant growth in untended forests, fields and other ecosystems. For example, "nitrogen is often in short enough supply that it's the primary controller of how much biomass is produced" in an ecosystem, he says. "If nitrogen is limited, the benefit of the CO2 increase is limited.... You can't just look at CO2, because the overall context really matters."

Det er en erfaring alle landmænd har gjort, nemlig at man ikke kan øge produktionen ved blot at tilføre et næringsstof

Planter lever af CO2. Vi får vores CO2 fra vores elproduktion, hvor det er et overskud, der i stedet for at skulle have været lukket ud af en skorsten, blæses ud i vores væksthuse

Kosmos skrev:

Det er en erfaring alle landmænd har gjort, nemlig at man ikke kan øge produktionen ved blot at tilføre et næringsstof

- dén viden må du hellere skynde dig at viderebringe til "Aroma tomater":

Planter lever af CO2. Vi får vores CO2 fra vores elproduktion, hvor det er et overskud, der i stedet for at skulle have været lukket ud af en skorsten, blæses ud i vores væksthuse

, så de snarest kan bringes ud af deres vildfarelse!