Pemanasan global: Perbedaan antara revisi

Terdapat [[hipotesis]] yang menyatakan bahwa variasi dari [[matahari]], dengan kemungkinan diperkuat oleh [[umpan balik]] dari [[awan]], dapat memberi kontribusi dalam pemanasan saat ini.<ref>{{cite journal | first=Nigel | last=Marsh | coauthors=Henrik, Svensmark | title=Cosmic Rays, Clouds, and Climate | journal=Space Science Reviews | volume=94 | number=1-2 | pages=215-230 | year=2000 | month=November | url=http://www.dsri.dk/~hsv/SSR_Paper.pdf | format=[[Portable Document Format|PDF]] | doi=10.1023/A:1026723423896 | accessdate=17-04-2007 | archive-date=2008-05-27 | archive-url=https://web.archive.org/web/20080527234228/http://www.dsri.dk/~hsv/SSR_Paper.pdf | dead-url=yes | issn=0038-6308}}</ref> Perbedaan antara mekanisme ini dengan pemanasan akibat [[efek rumah kaca]] adalah meningkatnya aktivitas [[matahari]] akan memanaskan [[stratosfer]] sebaliknya [[efek rumah kaca]] akan mendinginkan [[stratosfer]]. Pendinginan [[stratosfer]] bagian bawah paling tidak telah diamati sejak tahun 1960,<ref>{{cite web|title=Climate Change 2001:Working Group I: The Scientific Basis (Fig. 2.12)|url=http://www.grida.no/climate/ipcc_tar/wg1/fig2-12.htm|date=2001|accessdate=08-05-2007|archive-date=2016-06-02|archive-url=https://web.archive.org/web/20160602235858/http://www.grida.no/climate/ipcc_tar/wg1/fig2-12.htm|dead-url=yes}}</ref> yang tidak akan terjadi bila aktivitas [[matahari]] menjadi kontributor utama pemanasan saat ini. Penipisan [[lapisan ozon]] juga dapat memberikan efek pendinginan tersebut tetapi penipisan tersebut terjadi mulai akhir tahun [[1970-an]]. Fenomena [[variasi Matahari]] dikombinasikan dengan aktivitas [[gunung berapi]] mungkin telah memberikan efek pemanasan dari masa pra-industri hingga tahun 1950, serta efek pendinginan sejak tahun 1950.<ref>{{cite web | url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter9.pdf | format=[[Portable Document Format|PDF]] | title=Understanding and Attributing Climate Change | work=Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change | accessdate=20-05-2007 | date=07-05-2007 | publisher=[[Intergovernmental Panel on Climate Change]] | last=Hegerl | first=Gabriele C. | coauthors=''et al.'' | pages=690 | quote=Recent estimates (Figure 9.9) indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the seconds half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings | archive-date=2018-05-08 | archive-url=https://web.archive.org/web/20180508152907/http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter9.pdf | dead-url=yes }}</ref><ref>{{cite journal | last=Ammann | first = Caspar | coauthors =''et al.'' | date=06-04-2007 | title=Solar influence on climate during the past millennium: Results from ransient simulations with the NCAR Climate Simulation Model | journal=Proceedings of the National Academy of Sciences of the United States of America | volume=104 | issue=10 | pages=3713-3718 | url=http://www.pnas.org/cgi/reprint/104/10/3713 | quote=However, because of a lack of interactive ozone, the model cannot fully simulate features discussed in (44)." "While the NH temperatures of the high-scaled experiment are often colder than the lower bound from proxy data, the modeled decadal-scale NH surface temperature for the medium-scaled case falls within the uncertainty range of the available temperature reconstructions. The medium-scaled simulation also broadly reproduces the main features seen in the proxy records." "Without anthropogenic forcing, the 20th century warming is small. The simulations with only natural forcing components included yield an early 20th century peak warming of ≈0.2&nbsp;°C (≈1950 AD), which is reduced to about half by the end of the century because of increased volcanism.}}