Body zlomu (faktaoklimatu.cz)
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ABody zlomu - Ekosystémy [1/3]
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Text v graficeZdroj/LinkCitace ze zdroje
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Co jsou body zlomu? Pařížská dohoda deklaruje úsilí o to, aby "nárůst globální průměrné teploty výrazně nepřekročil hranici 1,5 °C". Jedním z hlavních důvodů pro stanovení této hranice je riziko překročení tzv. bodů zlomu (tipping points). Podobně jako větev snese určité zatížení než se zlomí, i některé části planetárního systému se mohou při postupujících klimatických změnách "zlomit" a přejít do kvalitativně odlišného stavu.

Body zlomu v ekosystémech. Zatímco při oteplení do 1,5 °C jsou z velkých planetárních systémů ohroženy pouze korálové útesy, při oteplení nad 2 °C se blížíme pravděpodobným bodům zlomu mnoha velkých planetárních systémů.
Potsdam institute for climate researchTipping elements are components of the Earth system of supra-regional scale which - in terms of background climate - are characterized by a threshold behavior. Once operating near a threshold, these components can be tipped into a qualitatively different state by small external perturbations. To compare them with the human body, tipping elements could be described as organs which drastically alter or stop their usual function if certain requirements, such as oxygen supply, are not sufficiently fulfilled.The threshold behavior is often based on self-reinforcing processes which, once tipped, can continue without further forcing. It is thus possible that the new state of a tipping element persists, even if the background climate falls back behind the threshold. The transition resulting from the exceedance of a system-specific tipping point can be either abrupt or gradual. Its large-scale environmental impacts could endanger the livelihood of millions of people.
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IPCC‘Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels’, recognising that this would significantly reduce the risks and impacts of climate change.
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Hodnoty oteplení jsou uváděny vzhledem k předindustriální době. Současná hodnota globálního oteplení je přibližně 1 °CIPCCThe multi-century period prior to the onset of large-scale industrial activity around 1750. The reference period 1850–1900 is used to approximate pre-industrial global mean surface temperature (GMST). See also Industrial revolution.
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1Severské jehličnaté lesy
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Severské jehličnaté lesy (tajga) jsou největší planetární ekosystém, pokrývající 11 % souše. Oteplování vede k většímu suchu, požárům, přežívání místních kůrovců apod., a tedy k postupné proměně tajgy v severskou step. EN WikipediaTaiga is the world's largest land biome [3] (depending on how one defines a biome, it could also be considered the second-largest, after deserts and xeric shrublands), covering 17 million square kilometres (6.6 million square miles) or 11.5% of the Earth's land area
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EN WikipediaWinter temperatures have increased more than summer temperatures. The number of days with extremely cold temperatures (e.g., −20 to −40 °C (−4 to −40 °F) has decreased irregularly but systematically in nearly all the boreal region, allowing better survival for tree-damaging insects ... In Siberia, the taiga is converting from predominantly needle-shedding larch trees to evergreen conifers in response to a warming climate. This is likely to further accelerate warming, as the evergreen trees will absorb more of the sun's rays. Given the vast size of the area, such a change has the potential to affect areas well outside of the region.[56] In much of the boreal forest in Alaska, the growth of white spruce trees are stunted by unusually warm summers, while trees on some of the coldest fringes of the forest are experiencing faster growth than previously.[57]
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Při oteplení o +3 až 4 °C dojde pravděpodobně k masivnímu úhynu stromů na většině území tajgy. IPCC SR15 CH3(page 263:) Increased disturbance from fire, pests and heat-related mortality may affect, in particular, the southern boundary of boreal forests (medium confidence) (Gauthier et al., 2015), with these impacts accruing with greater warming and thus impacts at 2°C would be expected to be greater than those at 1.5°C (medium confidence). A tipping point for significant dieback of the boreal forests is thought to exist, where increased tree mortality would result in the creation of large regions of open woodlands and grasslands which would favour further regional warming and increased fire frequencies, thus inducing a powerful positive feedback mechanism (Lenton et al., 2008; Lenton, 2012). This tipping point has been estimated to exist between 3°C and 4°C of global warming (low confidence) (Lucht et al., 2006; Kriegler et al., 2009), but given the complexities of the various forcing mechanisms and feedback processes involved, this is thought to be an uncertain estimate.
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2Tropické deštné pralesy
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V tropických deštných lesích Amazonie, Afriky a Indonésie žijí přibližně dvě třetiny rostlinných a živočišných druhů planety. Jsou ohroženy nejen kácením a požáry, ale i změnou v množství srážek v důsledku oteplení.en.wikipediaAround 40% to 75% of all biotic species are indigenous to the rainforests.[2] There may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests. ... Forests are being destroyed at a rapid pace.[36][37][38] Almost 90% of West Africa's rainforest has been destroyed.[39] Since the arrival of humans, Madagascar has lost two thirds of its original rainforest.[40] At present rates, tropical rainforests in Indonesia would be logged out in 10 years and Papua New Guinea in 13 to 16 years.
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en.wikipediaThe annual rate of deforestation in the Amazon region dramatically increased from 1991 to 2003.[12] In the nine years from 1991 to 2000, the total area of Amazon rainforest cleared since 1970 rose from 419,010 to 575,903 km2. (in year 2000) and the current cleared area is 792,051km2. (20% of original area in 1970)
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Při oteplení o +3 až 4 °C dojde pravděpodobně k masivnímu úhynu stromů na většině území deštných pralesů. Nezávisle na zvyšování teplot může dojít ke kolapsu ekosystému také při odlesnění asi 40 % plochy deštného pralesa.IPCC SR15 CH3(page 263:) A large portion of rainfall over the world’s largest rainforests is recirculated (e.g., Lenton et al., 2008), which raises the concern that deforestation may trigger a threshold in reduced forest cover, leading to pronounced forest dieback. For the Amazon, this deforestation threshold has been estimated to be 40% (Nobre et al., 2016). Global warming of 3°C–4°C may also, independent of deforestation, represent a tipping point that results in a significant dieback of the Amazon forest, with a key forcing mechanism being stronger El Niño events bringing more frequent droughts to the region (Nobre et al., 2016). Increased fire frequencies under global warming may interact with and accelerate deforestation, particularly during periods of El Niño-induced droughts (Lenton et al., 2008; Nobre et al., 2016). Global warming of 3°C is projected to reduce the extent of tropical rainforest in Central America, with biomass being reduced by about 40%, which can lead to a large replacement of rainforest by savanna and grassland (Lyra etal., 2017). Overall, modelling studies (Huntingford et al., 2013; Nobre et al., 2016) and observational constraints (Cox et al., 2013) suggest that pronounced rainforest dieback may only be triggered at 3°C–4°C (medium confidence), although pronounced biomass losses may occur at 1.5°C– 2°C of global warming.
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3Extrémní vlny veder
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Vlny veder se již nyní objevují na různých místech planety a ohrožují populace lidí i zvířat. Např. v lednu 2019 dosáhly teploty v Austrálii 45 °C, což vedlo k úhynu stovek tisíců kaloňů – vymřela přibližně třetina populace. Ztráta druhů rostlin či živočichů může vést ke kolapsům regionálních ekosystémů. en.wikipediaHigh temperatures have broken or nearly broken records in various cities across India and Pakistan. At one point, 11 of the 15 warmest places in the world were all located in the country.[18] On 2 June 2019, the city of Churu recorded a temperature of 50.8 °C (123.4 °F), only two-tenths of a degree Celsius short of the country's highest-ever temperature, 51 °C (124 °F) during the 2016 heat wave.[6] On 9 June 2019, Allahabad reached 48.9 °C (120.0 °F), breaking its previous all-time record.[18] On 3 and 4 June 2019, the temperature in Jacobabad reached 49 °C (120 °F) making Pakistan's highest-ever temperature
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BBCOver two days in November, record-breaking heat in Australia's north wiped out almost one-third of the nation's spectacled flying foxes, according to researchers. The animals, also known as spectacled fruit bats, were unable to survive in temperatures which exceeded 42C.
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ScienceDaily numbers of deaths at a regional level were collected in 16 European countries. Summer mortality was analyzed for the reference period 1998–2002 and for 2003. More than 70,000 additional deaths occurred in Europe during the summer 2003.
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Globání oteplování povede k častějším a intenzivnějším vlnám veder, zvýšení světové teploty o +2 °C povede v některých oblastech ke každoročnímu opakování smrtících vln veder. Další zvyšování teploty může způsobit, že se velké časti lidmi obývaných území stanou trvale neobyvatelné.IPCC SR15 CH3(page 242:) 2017). At 1.5°C of warming, twice as many megacities (such as Lagos, Nigeria, and Shanghai, China) than at present are likely to become heat stressed, potentially exposing more than 350 million more people to deadly heat stress by 2050. At 2°C of warming, Karachi (Pakistan) and Kolkata (India) could experience conditions equivalent to their deadly 2015 heatwaves on an annual basis (medium confidence). These statistics imply a tipping point in the extent and scale of heatwave impacts.
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Proceedings of National Academy of SciencesDespite the uncertainty in future climate-change impacts, it is often assumed that humans would be able to adapt to any possible warming. Here we argue that heat stress imposes a robust upper limit to such adaptation. Peak heat stress, quantified by the wet-bulb temperature TW, is surprisingly similar across diverse climates today. TW never exceeds 31 °C. Any exceedence of 35 °C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7 °C, calling the habitability of some regions into question. With 11–12 °C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12 °C are possible from fossil fuel burning. One implication is that recent estimates of the costs of unmitigated climate change are too low unless the range of possible warming can somehow be narrowed. Heat stress also may help explain trends in the mammalian fossil record.
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4Korálové útesy
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Korálové útesy jsou ohniska biodiversity – je na ně vázáno 25 % všech druhů mořských živočichů. Zároveň poskytují efektivní ochranu před rozbouřeným mořem, pohltí 97 % energie mořkých vln. V posledních letech způsobily nebývale teplé oceány zánik 50 % velkého bariérového útesu. EN WIKIPEDIAOften called "rainforests of the sea", shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species
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NATUREcoral reefs provide substantial protection against natural hazards by reducing wave energy by an average of 97%. Reef crests alone dissipate most of this energy (86%).
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IPCC SR15 CH3(page 226:) The current assessment also considered the heatwave-related loss of 50% of shallow-water corals across hundreds of kilometres of the world’s largest continuous coral reef system, the Great Barrier Reef.
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Při zvýšení teploty nad +1,2 °C nepřežijí téměř žádné ze současných korálových útesů.IPCC SR15 CH3(page 179:) For example, multiple lines of evidence indicate that the majority (70–90%) of warm water (tropical) coral reefs that exist today will disappear even if global warming is constrained to 1.5°C (very high confidence) (page 226:) Warm water (tropical) coral reefs are projected to reach a very high risk of impact at 1.2°C (Figure 3.18), with most available evidence suggesting that coral-dominated ecosystems will be non-existent at this temperature or higher (high confidence).
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