The Effects of Global Warming of 1.5°C on the

The Effects of Global Warming of 1.5°C on the Biosphere and its Associated Impacts on Human Activity, and the Scientific Basis for Limiting Global Warming to 1.5°C

Global warming of 1.5°C above pre-industrial levels will have adverse effects on all the major earth systems, with specific reference to the biosphere. It will also have associated negative impacts on human activity. The impacts of climate change will be exacerbated at a global warming of 2.0°C, and therefore it is crucial to limit global warming to 1.5°C. Human activity has resulted in an increase of 1.0°C in global temperatures and this is projected to increase to 1.5°C by 2030-2052 if the current rate of warming continues.

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Global warming of 1.5°C will affect the weather and climate of all the major biomes to an extent, with high latitude regions experiencing the greatest effects, a 2.0°C increase will exacerbate such effects. Climate and weather alteration include heavy precipitation in both frequency and duration in several northern hemisphere high-elevation regions e.g. eastern Asia and eastern North America, resulting in an increased risk of tropical cyclones and flooding. There will be a significant increase in terms of hot extremes for example in the Sahel, (Weber et al., 2018), with hot days experiencing an estimated increase of 3°C at 1.5°C of warming which increases to 4°C at 2.0°C of global warming. There is an increased risk of drought associated with rising temperatures and changes in precipitation (Sylla et al., 2015). 

Warming, however, is not continuous throughout the world, and land areas experience greater warming (Seneviratne et al., 2016), as does the Arctic which has encountered warming 2-3 times higher than the global average. This will affect sea levels which will have ensuing negative impacts on the biosphere and human activity. In high latitudes regions, for example, the arctic tundra, positive feedback mechanisms can result in further warming due to retreating of sea ice, earlier spring snowmelt, shrinking glaciers, and encroachment of woody shrubs within the tundra, lowering the albedo of the region, thus decreasing surface reflectivity and therefore amplifying high latitude warming (IPCC, 2007). The arctic tundra acts as a carbon sink with 14% of the world’s carbon estimated to be sequestrated in the permafrost and therefore, the risk of melting permafrost releasing this carbon into the atmosphere and perpetuating further global warming is a concern for climate change scientists. Global warming limited to an increase of 1.5°C will result in the thawing, over centuries, of 2.5million ${\mathrm{Km}}^2$

of permafrost, however the loss of permafrost is projected to be significantly higher at a global warming of 2.0°C  (Chadburn et al., 2017). At 1.5°C of global warming, there is predicted to be one ice-free arctic summer per summer, however, this increases to one per decade with 2°C of global warming (Jahn, 2018). Therefore, it is critical that global warming is limited to 1.5°C to minimise the melting of permafrost and shrinking of glaciers, which can have devastating impacts on both the biosphere and on human activity.

The livelihoods of indigenous communities inhabiting the arctic tundra are at risk to the effects of global warming. Indigenous tribes rely on hunting polar bears, walrus, seals, and caribou, and herding reindeer to support their local economy and is an essential aspect of their cultural and social identity. Global warming is likely to cause changes to the biodiversity of the arctic due to destruction of habitat, this will resultantly cause a change in the availability of traditional food sources. Reindeer herding is also under threat with reports of reindeers falling through thinning ice by Saami herders, and the annual pilgrimage of the Nenets in the Russian arctic was delayed due to thin ice. Therefore it is clear, the thinning ice poses a significant threat to the lives of the native people.

Taiga, also known as the boreal forest, is the wold’s largest biome and is another region particularly sensitive to the effects of climate change, likely to experience higher local warming than the global average (WGII AR5: Collins et 29 al., 201.). Boreal warming has been associated with a decline in greenness since 1990 as a result of increased drought, insect outbreaks, and wildfires (Zimov, 2006), the frequency and intensity of which, are magnified at 2.0°C. The number of days with extremely cold temperatures (−20 to −40 °C) has decreased systematically in nearly all the boreal region, allowing better survival for tree-damaging insects and there have been outbreaks of forest damaging plagues in recent years due to insect pests, for example, the spruce-bark beetle in Yukon and Alaska. Summer warming has resulted in regions such as Fairbanks, Alaska having a longer frost free season, reaching 120 days in contrast to 60-90 days in the previous century. This resultantly, has increased water stress impacting birch trees in the central Alaska region, and therefore it is clear warming has negative impacts on the biosphere.

Sea Level is projected to increase by up to 0.77m by 2100 at a global warming of 1.5°C, this is 0.1m lower than expected at a warming of 2.0°C, this reduction of 0.1m results in 10million fewer people being exposed to the related risks. Sea levels are expected to rise beyond 2100 and the magnitude of this increase is determined by future emission pathways (Church et al., 2013). Marine ice sheet instability in Antarctica and irreversible loss of the Greenland ice sheet could result in multi-meter rise in sea levels over thousands of years (Fuerst et al., 2015). A slower rise of sea levels will allow human and ecological systems to adapt especially those in small islands of low lying coastal regions and deltas. Risks associated with a rising sea level include saltwater intrusion, flooding, and damage to infrastructure. Impacts on biodiversity and ecosystems include species loss and extinction, however, the impacts on terrestrial, freshwater and coastal ecosystems are projected to be lower at 1.5°C in comparison to 2.0°C.

The biosphere will be greatly affected by climate change and according to international experts, global warming is likely to be the greatest cause of species extinctions this century with estimates indicating that a 1.5°C rise may put 20-30% of species at risk of extinction (WWF). At a global warming of 1.5°C, 6% of insects, 8% of plants and 4% of vertebrates are projected to lose over half of their climatically determined geographic range, this loss is doubled at a global warming of 2.0°C  (Warren et al., 2018b), and 13% of global terrestrial land area is projected to undergo a transformation of ecosystems from one type to another, this is 50% higher than the effects of 1.5°C of warming (Warszawski et al., 2013). Therefore, there is significant reasoning for limiting climate change to 1.5°C to help conserve biodiversity and the protection of species.

Coral reefs are an ecosystem especially at risk to the impacts of global warming, increased water temperatures and increasing ${\mathrm{CO}}_2$

concentrations mean that oceans are becoming more acidic. Sensitive coral species and algae are starved of oxygen, leading to bleaching and possibly even the death of the coral. At 1.5°C of warming 70-90% of corals are bleached however, this increases to >99% at 2.0°C of warming.  Fish and other marine organisms are subsequently affected, threatening an estimated half a billion people that rely on fish from coral reefs as their main source of protein.

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Lower risks to human health are projected at a global warming of 1.5°C in contrast to a 2.0°C warming. Urban heat islands often amplify the effects of heatwaves in cities and therefore heat-related morbidity and mortality increases at 2.0°C of warming (K.R. Smith et al., 2014). Increases of vector-borne diseases, for example, malaria and dengue fever, are projected as mosquitos invade higher latitude regions due to increased temperatures and shifts in precipitation levels, the effects of which will be again exacerbated at 2.0°C in contrast to a 1.5°C increase in global warming (IPCC, 2018).

Reductions in projected food availability are larger at 2.0°C than at 1.5°C of global warming, livestock are expected to be adversely affected by rising temperatures, due to changes in feed quality, spread of disease, and water resource availability (Kipling et al., 2016). Nutrient cycles are affected from rising temperatures,  and changes in precipitation levels, which has resulted in desertification in regions such as the Sahel,  this has subsequently affect nutrient replenishment and soil fertility. As a result, yields of maize, rice, and wheat, will experience significant reductions (Lobell et al., 2011). This will result in a diminished food security and may cause the number of food insecure people to increase – which is currently standing at 795 million.  Desertification results in land degradation which causes a decrease in biodiversity and thus affects the biosphere.

In conclusion, it is clear there is an imperative to limit global warming to 1.5°C to mitigate associated adverse effects, as it is understood that the impacts of global warming are amplified at an increase of 2.0°C. Global warming will have detrimental effects to both the biosphere and to human activity, coral reefs and indigenous communities are particularly vulnerable to such effects.

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