Query: A drop in volcanic activity caused warming.

Relevant passages:
Paleocene–Eocene Thermal Maximum <=SEP=> The Paleocene -- Eocene Thermal Maximum ( PETM ) , alternatively ( ETM1 ) , and formerly known as the `` Initial Eocene '' or '' '' was a time period with more than 8 ° C warmer global average temperature than today . This climate event began at the time boundary between the Paleocene and Eocene geological epochs . The exact age and duration of the event is uncertain but it is estimated to have occurred around 55.5 million years ago .   The associated period of massive carbon injection into the atmosphere has been estimated to have lasted no longer than 20,000 years . The entire warm period lasted for about 200,000 years . Global temperatures increased by 5 -- 8 ° C . The carbon dioxide was likely released in two pulses , the first lasting less than 2,000 years . Such a repeated carbon release is in line with current global warming . A main difference is that during the Paleocene -- Eocene Thermal Maximum , the planet was essentially ice-free .   The onset of the Paleocene -- Eocene Thermal Maximum has been linked to an initial 5 ° C temperature rise and to extreme changes in Earth 's carbon cycle . The period is marked by a prominent negative excursion in carbon stable isotope records from around the globe ; more specifically , there was a large decrease in 13C/12C ratio of marine and terrestrial carbonates and organic carbon .   Stratigraphic sections of rock from this period reveal numerous other changes . Fossil records for many organisms show major turnovers . For example , in the marine realm , a mass extinction of benthic foraminifera , a global expansion of subtropical dinoflagellates , and an appearance of excursion , planktic foraminifera and calcareous nanofossils all occurred during the beginning stages of PETM . On land , modern mammal orders ( including primates ) suddenly appear in Europe and in North America . Sediment deposition changed significantly at many outcrops and in many drill cores spanning this time interval .   At least since 1997 , the Paleocene -- Eocene Thermal Maximum has become a focal point of considerable geoscience research because it probably provides the best past analog by which to understand impacts of global climate warming and of massive carbon input to the ocean and atmosphere , including ocean acidification . Although it is now widely accepted that the PETM represents a `` case study '' for global warming and massive carbon input to Earth 's surface , the cause , details and overall significance of the event remain perplexing .

Triassic–Jurassic extinction event <=SEP=> The Triassic -- Jurassic extinction event marks the boundary between the Triassic and Jurassic periods , , and is one of the major extinction events of the Phanerozoic eon , profoundly affecting life on land and in the oceans . In the seas , a whole class ( conodonts ) and 34 % of marine genera disappeared . On land , all archosaurs other than crocodylomorphs ( Sphenosuchia and Crocodyliformes ) and Avemetatarsalia ( pterosaurs and dinosaurs ) , some remaining therapsids , and many of the large amphibians became extinct .

1257 Samalas eruption <=SEP=> The 1257 Samalas eruption was a major volcanic eruption of the Samalas volcano , next to Mount Rinjani on the island of Lombok , Indonesia . It left a large caldera next to Rinjani volcano , the lake Segara Anak . This volcanic eruption reached a volcanic explosivity index of 7 , making it one of the largest eruptions of the Holocene . The occurrence of this eruption was originally deduced from ice core information revealing a spike in sulfate deposition around the year 1257 ; in 2013 the source of this eruption at Samalas was definitively proven as a result of historical records from that time .   This eruption proceeded during four distinct phases , alternately creating eruption columns reaching up for tens of kilometres and pyroclastic flows that buried large parts of Lombok , destroying human habitations including the city of Pamatan . Ash from the eruption fell as far as Java . The volume of the deposits left exceeds 10 km3 . Later activity from the volcano created additional volcanic centres in the caldera , including the present day active Barujari cone .   The eruption was witnessed by humans on Lombok , who recorded its effects on text written on palm leaves . The aerosols injected by the volcano into the atmosphere reduced the solar radiation reaching the surface of the Earth , triggering a volcanic winter and cooling lasting for several years . It is possible that the 1257 Samalas eruption helped trigger the Little Ice Age .

Global warming <=SEP=> Global warming , also referred to as climate change , is the observed century-scale rise in the average temperature of the Earth 's climate system and its related effects . Multiple lines of scientific evidence show that the climate system is warming . Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid 19th century , and in paleoclimate proxy records over thousands of years .   In 2013 , the Intergovernmental Panel on Climate Change ( IPCC ) Fifth Assessment Report concluded that `` It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century . '' The largest human influence has been emission of greenhouse gases such as carbon dioxide , methane and nitrous oxide . Climate model projections summarized in the report indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to for their lowest emissions scenario and 2.6 to for the highest emissions scenario . These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing .   Future climate change and associated impacts will differ from region to region around the globe . Anticipated effects include warming global temperature , rising sea levels , changing precipitation , and expansion of deserts in the subtropics . Warming is expected to be greater over land than over the oceans and greatest in the Arctic , with the continuing retreat of glaciers , permafrost and sea ice . Other likely changes include more frequent extreme weather events including heat waves , droughts , heavy rainfall with floods and heavy snowfall ; ocean acidification ; and species extinctions due to shifting temperature regimes . Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels . Because the climate system has a large `` inertia '' and greenhouse gases will stay in the atmosphere for a long time , many of these effects will not only exist for decades or centuries , but will persist for tens of thousands of years .   Possible societal responses to global warming include mitigation by emissions reduction , adaptation to its effects , building systems resilient to its effects , and possible future climate engineering . Most countries are parties to the United Nations Framework Convention on Climate Change ( UNFCCC ) ,  whose ultimate objective is to prevent dangerous anthropogenic climate change . Parties to the UNFCCC have agreed that deep cuts in emissions are required and that global warming should be limited to well below 2.0 C-change relative to pre-industrial levels , with efforts made to limit warming to 1.5 C-change .   Public reactions to global warming and concern about its effects are also increasing . A global 2015 Pew Research Center report showed a median of 54 % consider it `` a very serious problem '' . There are significant regional differences , with Americans and Chinese ( whose economies are responsible for the greatest annual CO2 emissions ) among the least concerned .