Some models
include volcanic effects by simply perturbing the incoming shortwave radiation at the top of the atmosphere, while others simulate explicitly the radiative effects of the aerosols in the stratosphere.
In the real world, forcings (as estimated by GISS and not
including volcanic effects) increased at 0.36 W / m2 per decade (1990 to 2003).
Not exact matches
One just
included the effective influence on temperatures from manmade forces (
including greenhouse gases and aerosols, which tend to have a cooling
effect), while the second
included both manmade and natural ones (
including volcanic activity and solar radiation).
Here, we show that the effective solar radiation (ESR), which
includes the net solar radiation and the
effects of
volcanic eruption, has modulated this decadal ENSO - like oscillation.
Over the last 30 years of direct satellite observation of the Earth's climate, many natural influences
including orbital variations, solar and
volcanic activity, and oceanic conditions like El Nino (ENSO) and the Pacific Decadal Oscillation (PDO) have either had no
effect or promoted cooling conditions.
In Earth's past the trigger for these greenhouse gas emissions was often unusually massive
volcanic eruptions known as «Large Igneous Provinces,» with knock - on
effects that
included huge releases of CO2 and methane from organic - rich sediments.
Human induced trend has two components, namely (a) greenhouse
effect [this
includes global and local / regional component] and (b) non-greenhouse
effect [local / regional component]-- according to IPCC (a) is more than half of global average temperature anomaly wherein it also
includes component of
volcanic activities, etc that comes under greenhouse
effect; and (b) contribution is less than half — ecological changes component but this is biased positive side by urban - heat - island
effect component as the met network are concentrated in urban areas and rural - cold - island
effect is biased negative side as the met stations are sparsely distributed though rural area is more than double to urban area.
The absence of convincing attribution of periods other than 1976 - present to anthropogenic forcing leaves natural climate variability as the cause — some combination of solar (
including solar indirect
effects), uncertain
volcanic forcing, natural internal (intrinsic variability) and possible unknown unknowns.
These variables
include volcanic outgassing, Malankovich cycles, tectonic plate movements, solar variability, meteor impacts, comet tails, albedo, oceanic circulation, topography, a variety of hidden threshold
effects, biological evolution and human technology.»
Assuming that the change is all solar would lead to a doubling of the solar impact, thus
including long term
volcanic effects is important.
The linear
effects that ENSO and
volcanic aerosols have on global temperatures are well documented through a multitude of different analyses,
including «curve - fitting».
For instance, the warming that began in the early 20th century (1925 - 1944) is consistent with natural variability of the climate system (
including a generalized lack of significant
volcanic activity, which has a cooling
effect), solar forcing, and initial forcing from greenhouse gases.
Other factors than warming that could have temporarily lowered Greenland ice reflectivity
include the
effect of major
volcanic eruptions or wild fires.
For example, the accumulated
effect of
volcanic eruptions during the past decade,
including the Icelandic volcano with the impossible name, Eyjafjallajökull, may have had a greater cooling
effect on the earth's surface than has been accounted for in most climate model simulations.
Natural variations in climate
include the
effects of cycles such as El Niño, La Niña and other ocean cycles; the 11 - year sunspot cycle and other changes in energy from the sun; and the
effects of
volcanic eruptions.
A fairer comparsion would involve also adjusting the observations to account for the
effects of internal variablity (e.g. by regression analysis to remove the
effects of ENSO and
volcanic forcings which the models do not
include).
Instead of responding only to the cooler temperatures, the tree rings also
included signals from reduced light availability (from the shading
effect of
volcanic aerosols) and the two
effects together produced a signal greater than what would have been produced by cooler temperatures alone.
But not only did Michaels make no mention of Scenarios B & C, he also never mentioned that Hansen's paper
included the cooling
effect of a major
volcanic eruption (in Scenarios B & C) nor did he make any mention that one in fact occurred — Mt. Pinatubo (and neither does O» Donnell, at least the part you quoted).
Possible explanations advanced for the slowdown
include the
effect of small
volcanic eruptions, the absorption of extra heat by the oceanic depths and the juxtaposition of two natural ocean cycles.
The model
included a more comprehensive set of natural and human - made climate forcings than previous studies,
including changes in solar radiation,
volcanic particles, human - made greenhouse gases, fine particles such as soot, the
effect of the particles on clouds and land use.
Projections of future climate do not typically
include the
effects of
volcanic activity.
Proposals for addressing global warming now
include geo - engineering whereby tiny particles are injected into the stratosphere to emulate the cooling
effects of stratospheric aerosol of a
volcanic eruption (Levitt and Dubner 2009).