IPCC 1.5? Laporan: Inilah Yang Dikatakan Sains Iklim

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Para saintis iklim dunia telah bercakap: jika kita mahu mengehadkan pemanasan global yang disebabkan oleh manusia kepada 1.5? kita mungkin boleh. Tetapi ia akan menjadi sukar, memandangkan dari mana kita bermula.

Itulah kesimpulan a laporan baru by the UN’s Intergovernmental Panel on Climate Change (IPCC). The focus on 1.5? is the result of years of international negotiation. Starting in 1994, a central aim of the UN’s climate change efforts (the Framework Convention on Climate Change, or UNFCCC) was to stabilise greenhouse gas concentrations at a level that would “prevent dangerous anthropogenic interference with the climate system”. Much was written on what this meant, particularly the word “dangerous”.

Impak negatif perubahan iklim berlaku pada satu kontinum, dan menentukan satu titik di mana perubahan iklim menjadi berbahaya adalah sukar dan perbalahan. Sebaliknya, rundingan perubahan iklim adalah sukar tanpa sasaran untuk bekerja.

Fifteen years later, the UNFCCC’s Copenhagen Accord introduced a 2? target, and its 2015 Perjanjian Paris was even more specific: it “aims to strengthen the global response to the threat of climate change … by holding the increase in … temperature to well below 2? above pre-industrial levels and pursuing efforts to limit the … increase to 1.5?”.

IPCC menyediakan nasihat saintifik kepada UNFCCC, yang membuat dasar, dan IPCC itu sendiri tidak pernah menyatakan sasaran suhu. Walau bagaimanapun, ia menyenaraikan risiko perubahan iklim menggunakan lima "sebab untuk kebimbangan". Ini termasuk kesan seperti "ekosistem dan budaya yang unik dan terancam" (seperti terumbu karang) dan "peristiwa cuaca yang melampau", yang masing-masing dinilai pada skala dari "tidak dapat dikesan" hingga "sangat tinggi". IPCC paling terkini (2014) Penilaian Kelima of the scientific evidence found that at around 1.5? warming there was a transition dari risiko sederhana hingga tinggi untuk ekosistem dan budaya yang terancam dan peristiwa cuaca yang melampau. Oleh itu, ada konsistensi antara penilaian Paris dan IPCC.


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IPCC 1.5? Laporan: Inilah Yang Dikatakan Sains IklimPerubahan iklim akan menjadikan beberapa jenis cuaca ekstrim lebih biasa. Drew McArthur / Shutterstock

The Paris Agreement asked the IPCC to report on the impacts of global warming of 1.5?, and this new publication is the result. Its tone is not “we must avoid 1.5? warming”, as you might think from many commentators, but more “if we want to avoid 1.5? warming, this is what must be done”. The report contrasts the impact of 1.5? and 2? warmings, giving information on what would be gained by the extra effort needed to limit warming to 1.5?.

As the IPCC’s reports are largely based on a critical assessment and synthesis of published scientific papers, many of its latest conclusions are unsurprising. There are many well recognised uncertainties in understanding climate change - for instance, even if we set a course aiming to hit 1.5? (which is mostly determined by future CO? emissions), we could end up hitting, say, 1? or 2? instead. The report provides uncertainty ranges in its estimates and confidence levels, based on expert judgement.

The new report tells us that human activity has already caused about 1? of global warming, while at the present rate of warming (0.2? per decade) we’ll hit 1.5? by about 2040. National pledges made as part of the Paris Agreement still mean we are on course for warming of about 3? by 2100, meaning four of the five “reasons for concern” would then be in the high to very-high risk category.

Achieving the 1.5? target will require anthropogenic CO? emissions to decline by 45% by 2030 (relative to 2010). By 2050, they will need to reach “net zero” - any further CO? emissions due to human activity would then have to be matched by penyingkiran sengaja of CO? already in the atmosphere, including by planting trees. Net zero would have to occur by around 2075 to meet a 2? target.

IPCC 1.5? Laporan: Inilah Yang Dikatakan Sains Iklim Projek penghutanan semula di Thailand. Somrerk Witthayanantw / Shutterstock

Many illustrations are given for the difference between 1.5? and 2? worlds. At 1.5?, summertime Arctic sea ice is projected to disappear once per century, compared to once per decade at 2?; 8% of plants that have been studied would lose half their climatically-suitable area, compared to 16%; sea level rise would be 10cm less (with 10m fewer people impacted at today’s population levels); and while coral reefs might decline by a further 80% at 1.5?, they could virtually disappear at 2?.

The report identifies various routes by which emissions cuts would limit warming to 1.5?; each makes assumptions about future changes in, for example, economic strategy, population growth and the rate at which low carbon energy is adopted. The IPCC recognises the challenges are “unprecedented in scale” but notes, for example, “the feasibility of solar energy, wind energy and electricity storage mechanisms have substantially improved over the past few years”.

The report is sensitive to the fact that changes required to meet 1.5? must be consistent with the UN’s wider matlamat pembangunan mampan. Mengehadkan perubahan iklim akan membantu memenuhi matlamat yang berkaitan dengan kesihatan, tenaga bersih, bandar dan lautan. Tetapi ada potensi kesan negatif terhadap orang lain (kemiskinan, kelaparan, air, akses tenaga) "jika tidak dikendalikan dengan teliti".

Jadi di mana seterusnya? Sudah tentu, kesimpulan akan dibahaskan secara meluas di banyak peringkat, tetapi mata akan menjadi respon UNFCCC pada mesyuarat berikutnya, di Katowice, Poland, pada awal Disember.Perbualan

Tentang Pengarang

Keith Shine, Profesor Meteorologi dan Sains Iklim Regius, Universiti Reading

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