Hidup di zaman rumah kaca terakhir di planet ini, Eosen. Museum Jay Matternes / Smithsonian, CC BYHidup di zaman rumah kaca terakhir di planet ini, Eosen. Museum Jay Matternes / Smithsonian, CC BY

Konsentrasi karbon dioksida menuju nilai yang tidak terlihat pada tahun-tahun sebelumnya 200m. Matahari juga berangsur-angsur semakin kuat seiring berjalannya waktu. Bersama-sama, fakta-fakta ini berarti iklim mungkin menuju kehangatan yang tidak terlihat dalam setengah miliar tahun terakhir. Percakapan

A lot has happened on Earth since 500,000,000BC – continents, oceans and mountain ranges have come and gone, and complex life has evolved and moved from the oceans onto the land and into the air. Most of these changes occur on very long timescales of millions of years or more. However, over the past 150 years global temperatures have increased by about 1?, ice caps and glaciers have retreated, polar sea-ice has melted, and sea levels have risen.

Beberapa akan menunjukkan bahwa iklim bumi telah ada mengalami perubahan serupa sebelumnya. Jadi, apa masalahnya?

Para ilmuwan dapat mencoba memahami iklim masa lalu dengan melihat bukti yang terkurung di batuan, sedimen dan fosil. Apa yang dikatakan ini adalah bahwa ya, iklim telah berubah di masa lalu, namun kecepatan perubahan saat ini adalah sangat tidak biasa. Misalnya, karbon dioksida belum ditambahkan ke atmosfer secepat hari ini setidaknya untuk masa lalu 66m tahun.


grafis berlangganan batin


In fact, if we continue on our current path and exploit all convention fossil fuels, then as well as the rate of CO? emissions, the absolute climate warming is also likely to be unprecedented in at least the past 420m years. That’s according to a new study we have published in Alam Komunikasi.

In terms of geological time, 1? of global warming isn’t particularly unusual. For much of its history the planet was significantly warmer than today, and in fact more often than not Earth was in what is termed a “greenhouse” climate state. During the last greenhouse state 50m years ago, global average temperatures were 10-15? warmer than today, the polar regions were ice-free, Pohon palem tumbuh di pesisir Antartika, dan buaya dan kura-kura yang dikebiri di hutan rawa-rawa di daerah Arktik Kanada yang beku.

Sebaliknya, terlepas dari pemanasan saat ini, kita masih secara teknis berada dalam keadaan iklim "eshouse", yang berarti ada es di kedua kutub tersebut. Bumi secara alami mengayuh antara dua negara iklim ini setiap 300m bertahun-tahun atau lebih.

Just prior to the industrial revolution, for every million molecules in the atmosphere, about 280 of them were CO? molecules (280 parts-per-million, or ppm). Today, due primarily to the burning of fossil fuels, concentrations are about 400 ppm. In the absence of any efforts to curtail our emissions, burning of conventional fossil fuels will cause CO? concentrations to be around 2,000ppm by the year 2250.

This is of course a lot of CO?, but the geological record tells us that the Earth has experienced similar concentrations several times in the past. For instance, our new compilation of data shows that during the Triassic, around 200m years ago, when dinosaurs first evolved, Earth had a greenhouse climate state with atmospheric CO? around 2,000-3,000ppm.

Konsentrasi karbon dioksida yang tinggi sehingga tidak membuat dunia benar-benar tidak dapat dihuni. Dinosaurus berkembang pesat.

Itu tidak berarti ini bukan masalah besar. Sebagai permulaan, tidak ada keraguan bahwa umat manusia akan menghadapi tantangan sosial ekonomi utama yang dihadapi perubahan iklim yang dramatis dan cepat yang akan dihasilkan dari kenaikan pesat ke 2,000 atau lebih ppm.

But our new study also shows that the same carbon concentrations will cause more warming in future than in previous periods of high carbon dioxide. This is because the Earth’s temperature does not just depend on the level of CO? (or other greenhouse gases) in the atmosphere. All our energy ultimately comes from the sun, and due to the way the sun generates energy through nuclear fusion of hydrogen into helium, its brightness has increased over time. Four and a half billion years ago when the Earth was young the sun was around 30% less bright.

So what really matters is the combined effect of the sun’s changing strength and the varying greenhouse effect. Looking through geological history we generally found that as the sun became stronger through time, atmospheric CO? gradually decreased, so both changes cancelled each other out on average.

Tapi bagaimana dengan di masa depan? Kami tidak menemukan periode masa lalu ketika pengemudi iklim, atau iklim memaksa, setinggi mungkin di masa depan jika kita membakar semua bahan bakar fosil yang tersedia. Tidak ada yang seperti itu yang tercatat dalam rekaman rock setidaknya selama 420m tahun.

Sebuah pilar utama ilmu geologi adalah prinsip uniformitarian: that “the present is the key to the past”. If we carry on burning fossil fuels as we are at present, by 2250 this old adage is sadly no longer likely to be true. It is doubtful that this high-CO? future will have a counterpart, even in the vastness of the geological record.

Tentang Penulis

Gavin Foster, Profesor Geokimia Isotop, University of Southampton; Dana Royer, Guru Besar Ilmu Bumi dan Lingkungan, Universitas Wesleyan, dan Dan Lunt, Profesor Ilmu Iklim, University of Bristol

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