Query: Volcanoes have had no warming effect in recent global warming - if anything, a cooling effect.

Relevant passages:
Michael E. Mann <=SEP=> Michael E. Mann ( born 1965 ) is an American climatologist and geophysicist , currently director of the Earth System Science Center at Pennsylvania State University , who has contributed to the scientific understanding of historic climate change based on the temperature record of the past thousand years . He has pioneered techniques to find patterns in past climate change , and to isolate climate signals from noisy data .   As lead author of a paper produced in 1998 with co-authors Raymond S. Bradley and Malcolm K. Hughes , Mann used advanced statistical techniques to find regional variations in a hemispherical climate reconstruction covering the past 600 years . In 1999 the same team used these techniques to produce a reconstruction over the past 1,000 years ( MBH99 ) which was dubbed the `` hockey stick graph '' because of its shape . He was one of eight lead authors of the `` Observed Climate Variability and Change '' chapter of the Intergovernmental Panel on Climate Change ( IPCC ) Third Scientific Assessment Report published in 2001 . A graph based on the MBH99 paper was highlighted in several parts of the report , and was given wide publicity . The IPCC acknowledged that his work , along with that of the many other lead authors and review editors , contributed to the award of the 2007 Nobel Peace Prize , which was won jointly by the IPCC and Al Gore .   Mann was organizing committee chair for the National Academy of Sciences Frontiers of Science in 2003 and has received a number of honors and awards including selection by Scientific American as one of the fifty leading visionaries in science and technology in 2002 . In 2012 he was inducted as a Fellow of the American Geophysical Union and was awarded the Hans Oeschger Medal of the European Geosciences Union . In 2013 he was elected a Fellow of the American Meteorological Society , and awarded the status of distinguished professor in Penn State 's College of Earth and Mineral Sciences .   Mann is author of more than 200 peer-reviewed and edited publications . He has also published three books : Dire Predictions : Understanding Global Warming ( 2008 ) , The Hockey Stick and the Climate Wars : Dispatches from the Front Lines ( 2012 ) , and , together with co-author Tom Toles , The Madhouse Effect : How Climate Change Denial Is Threatening Our Planet , Destroying Our Politics , and Driving Us Crazy ( 2016 ) . In 2012 , the European Geosciences Union described his publication record as `` outstanding for a scientist of his relatively young age '' . Mann is also a co-founder and contributor to the climatology blog RealClimate .

Nuclear winter <=SEP=> Nuclear winter is the severe global-climatic-cooling-effect , hypothesized to occur after the ignition of a number of firestorms , from nuclear bomb detonations , or wide spread bombardments . Such fires , which can inject soot into the stratosphere , have historically occurred in a number of cities , with nuclear winter researchers using both Hamburg and the less ferocious Hiroshima firestorms as the principal examples . However , as firestorms are most frequently encountered in much larger area wildfires , these latter fires are the most significant today in assessing both the initial and present-day `` nuclear winter '' computer models .

Greenhouse effect <=SEP=> The greenhouse effect is the process by which radiation from a planet 's atmosphere warms the planet 's surface to a temperature above what it would be without its atmosphere .   If a planet 's atmosphere contains radiatively active gases ( i.e. , greenhouse gases ) the atmosphere will radiate energy in all directions . Part of this radiation is directed towards the surface , warming it . The downward component of this radiation -- that is , the strength of the greenhouse effect -- will depend on the atmosphere 's temperature and on the amount of greenhouse gases that the atmosphere contains .   On Earth , the atmosphere is warmed by absorption of infrared thermal radiation from the underlying surface ( heated by the sun ) , absorption of shorter wavelength radiant energy from the sun , and convective heat fluxes from the surface . Greenhouse gases in the atmosphere radiate energy , some of which is directed to the surface and lower atmosphere . The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect .   Earth 's natural greenhouse effect is critical to supporting life . Human activities , primarily the burning of fossil fuels and clearing of forests , have intensified the natural greenhouse effect , causing global warming .   The mechanism is named after a faulty analogy with the effect of solar radiation passing through glass and warming a greenhouse . The way a greenhouse retains heat is fundamentally different , as a greenhouse works by reducing airflow and retaining warm air inside the structure .

Ice age <=SEP=> An ice age is a period of long-term reduction in the temperature of Earth 's surface and atmosphere , resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers . Within a long-term ice age , individual pulses of cold climate are termed `` glacial periods '' ( or alternatively `` glacials '' or `` glaciations '' or colloquially as `` ice age '' ) , and intermittent warm periods are called `` interglacials '' . In the terminology of glaciology , ice age implies the presence of extensive ice sheets in both northern and southern hemispheres . By this definition , we are in an interglacial period -- the Holocene -- of the ice age . The ice age began 2.6 million years ago at the start of the Pleistocene epoch , because the Greenland , Arctic , and Antarctic ice sheets still exist .

Volcano <=SEP=> A volcano is a rupture in the crust of a planetary-mass object , such as Earth , that allows hot lava , volcanic ash , and gases to escape from a magma chamber below the surface .   Earth 's volcanoes occur because its crust is broken into 17 major , rigid tectonic plates that float on a hotter , softer layer in its mantle . Therefore , on Earth , volcanoes are generally found where tectonic plates are diverging or converging , and most are found underwater . For example , a mid-oceanic ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates pulling apart ; the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates coming together . Volcanoes can also form where there is stretching and thinning of the crust 's , e.g. , in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America . This type of volcanism falls under the umbrella of `` plate hypothesis '' volcanism . Volcanism away from plate boundaries has also been explained as mantle plumes . These so-called `` hotspots '' , for example Hawaii , are postulated to arise from upwelling diapirs with magma from the core -- mantle boundary , 3,000 km deep in the Earth . Volcanoes are usually not created where two tectonic plates slide past one another .   Erupting volcanoes can pose many hazards , not only in the immediate vicinity of the eruption . One such hazard is that volcanic ash can be a threat to aircraft , in particular those with jet engines where ash particles can be melted by the high operating temperature ; the melted particles then adhere to the turbine blades and alter their shape , disrupting the operation of the turbine . Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth 's lower atmosphere ( or troposphere ) ; however , they also absorb heat radiated up from the Earth , thereby warming the upper atmosphere ( or stratosphere ) . Historically , so-called volcanic winters have caused catastrophic famines .