The longwave part of
the net radiative change includes the «greenhouse effect» (i.e. the atmosphere radiating energy downward) and the longwave feedback (i.e. warmer things radiate more energy away).
Not exact matches
While a relatively minor part of the overall aerosol mass,
changes in the anthropogenic portion of aerosols since 1750 have resulted in a globally averaged
net radiative forcing of roughly -1.2 W / m2, in comparison to the overall average CO2 forcing of +1.66 W / m2.
In addition, researchers calculated the
changes in the shortwave and longwave and
net radiation between the pre-industrial simulation and the present - day simulations to estimate the
radiative forcing resulting from the aerosol effects on cirrus clouds.
That's far from the worst flaw in his calculation, since his two biggest blunders are the neglect of the
radiative cooling due to sulfate aerosols (known to be a critical factor in the period in question) and his neglect of the many links in the chain of physical effects needed to translate a top of atmosphere
radiative imbalance to a
change in
net surface energy flux imbalance.
While the local, seasonal climate forcing by the Milankovitch cycles is large (of the order 30 W / m2), the
net forcing provided by Milankovitch is close to zero in the global mean, requiring other
radiative terms (like albedo or greenhouse gas anomalies) to force global - mean temperature
change.
Gerald Marsh offered this opinion in «A Global Warming Primer» (page 4 - excerpt) «
Radiative forcing is defined as the change in net downward radiative flux at the tropopause resulting from any process that acts as an external agent to the climate system; it is generally measured i
Radiative forcing is defined as the
change in
net downward
radiative flux at the tropopause resulting from any process that acts as an external agent to the climate system; it is generally measured i
radiative flux at the tropopause resulting from any process that acts as an external agent to the climate system; it is generally measured in W / m2.
Some of that would result also in a
change in the radiation to space, and in particular a
change in the
net top of atmosphere
radiative imbalance.
In fact, all climate models do predict that the
change in globally - averaged steady state temperature, at least, is almost exactly proportional to the
change in
net radiative forcing, indicating a near - linear response of the climate, at least on the broadest scales.
Radiative forcing RF at a level is equal to a decrease in
net upward flux (either SW, LW, or both; the greenhouse effect refers to LW forcing) at that given level, due to a
change in (optical) properties, while holding temperatures constant.
The system can have a
net negative feedback and still
change very much provided a
radiative forcing from sunlight or CO2 is sufficiently large, although for typical
changes in these variables that Earth encounters, one would indeed expect only relatively small climate
changes to occur if negative feedbacks did in fact dominate.
Currently, although only 20 % of the accumulated anthropogenic rise in carbon dioxide originates from land use and land cover
change (LULCC), 40 % of the
net positive
radiative forcing from human activities is attributable to LULCC sources (Ward et al 2014).
The effect of band widenning is a reduction in
net upward LW flux (this is called the
radiative forcing), which is proportional to a
change in area under the curve (a graph of flux over the spectrum); the contribution from band widenning is equal to the amount by which the band widens (in units ν) multiplied by - Fνup (CO2).
«
Radiative forcing Radiative forcing is the change in the net, downward minus upward, radiative flux (expressed in W m — 2) at the tropopause or top of atmosphere due to a change in an external driver of climate change, such as, for example, a change in the concentration of carbon dioxide or the output of the Su
Radiative forcing
Radiative forcing is the change in the net, downward minus upward, radiative flux (expressed in W m — 2) at the tropopause or top of atmosphere due to a change in an external driver of climate change, such as, for example, a change in the concentration of carbon dioxide or the output of the Su
Radiative forcing is the
change in the
net, downward minus upward,
radiative flux (expressed in W m — 2) at the tropopause or top of atmosphere due to a change in an external driver of climate change, such as, for example, a change in the concentration of carbon dioxide or the output of the Su
radiative flux (expressed in W m — 2) at the tropopause or top of atmosphere due to a
change in an external driver of climate
change, such as, for example, a
change in the concentration of carbon dioxide or the output of the Sun.»
Then, if compositional
changes occur, involving
changes in the
net radiative balance of the entire atmosphere the climate zones will shift as the atmosphere has to work more hard or less hard to maintain top of atmosphere energy balance.
It clearly states that (a) emission of energy by radiation is accompanied with cooling of the surface (if no compensating
changes prevent it), and (b) the tendency to a
radiative equilibrium means that the emitter with the higher surface temperature will loose energy due to a negative
net radiation balance until this
net radiation balance becomes zero.
The albedo
change resulting from the snowline retreat on land is similarly large as the retreat of sea ice, so the combined impact could be well over 2 W / sq m. To put this in context, albedo
changes in the Arctic alone could more than double the
net radiative forcing resulting from the emissions caused by all people of the world, estimated by the IPCC to be 1.6 W / sq m in 2007 and 2.29 W / sq m in 2013.»
Relationships between the
change in
net top - of - atmosphere
radiative flux, N, and global - mean surface - air - temperature
change, ΔT, after an instantaneous quadrupling of CO2.
radiative forcing a
change in average
net radiation at the top of the troposphere resulting from a
change in either solar or infrared radiation due to a
change in atmospheric greenhouse gases concentrations; perturbance in the balance between incoming solar radiation and outgoing infrared radiation
Yes, the
change is incremental, and yes it's difficult to foresee sufficient incremental
change to reach a carbon neutral future, but it's a bigger impact than I think your colleague anticipates (disclosure: I didn't read his entire report carefully, but I didn't see anything that looks like a carbon balance or
net radiative forcing calculation).
The comparable
net change in
radiative forcings illustrated in AR4 WG1 Figure 2.23, as used by another GCM, seems to be even higher, at around 1 Wm - 2 between 1861 — 1900 and 1957 — 1994.
A comparison of CO2 and CH4 fluxes from eutrophic reservoirs suggests that eutrophication does little to
change the
net carbon balance of reservoirs, but greatly increases the atmospheric
radiative forcing caused by these systems through the stimulation of CH4 production (figure 3).
Irrespective of what one thinks about aerosol forcing, it would be hard to argue that the rate of
net forcing increase and / or over-all
radiative imbalance has actually dropped markedly in recent years, so any
change in
net heat uptake can only be reasonably attributed to a bit of natural variability or observational uncertainty.
To clarify, consider the
change in the
net radiative balance at the surface as having a shortwave and longwave component
The TOA imbalance minus the
net surface flux (from * all * fluxes, latent,
radiative, etc.) gives the rate of
change of the atmospheric energy content.
Radiative forcing -
Radiative forcing is the
change in the
net, downward minus upward, irradiance (expressed in W m - 2) at the tropopause due to a
change in an external driver of climate
change, such as, for example, a
change in the concentration of carbon dioxide or the output of the Sun.
Rather, Y is the slope coefficient for an (approximately) linear dependence of
net radiative balance N, minus the
change in forcings Q, on
changes deltaT in mean surface temperature.
IPCC AR4 WG1 tells us that the all anthropogenic forcing components except CO2 (aerosols, other GHGs, land use
changes, other
changes in surface albedo, etc.) have essentially cancelled one another out, so we can use the estimated
radiative forcing for CO2 (1.66 W / m ^ 2) to equate with total
net anthropogenic forcing (1.6 W / m ^ 2).
The ordinary least squares (OLS) regression approach used will, however, underestimate Y in the presence of fluctuations in surface temperature that do not give rise to
changes in
net radiative flux fitting the linear model.
This is achieved through the study of three independent records, the
net heat flux into the oceans over 5 decades, the sea - level
change rate based on tide gauge records over the 20th century, and the sea - surface temperature variations... We find that the total
radiative forcing associated with solar cycles variations is about 5 to 7 times larger than just those associated with the TSI variations, thus implying the necessary existence of an amplification mechanism, although without pointing to which one.
I tried to bring out the point about internal cloud oscillations, in writing: «The ordinary least squares (OLS) regression approach used will, however, underestimate Y in the presence of fluctuations in surface temperature that do not give rise to
changes in
net radiative flux fitting the linear model.
The effects of aerosols and landuse
changes reduce
radiative forcing so that the
net forcing of human activities is in the range of 311 to 435 ppm CO2 - eq, with a central estimate of about 375 ppm CO2 - eq.»
The
net radiative feedback due to all cloud types is likely (> 66 % chance) positive, although a negative feedback (damping global climate
changes) is still possible.
They found that
changes in atmospheric ionization during the 11 - year solar cycle, and the resulting variations in aerosol formation, produced a globally asymmetric
radiative forcing with a
net cloud albedo effect of − 0.05 W m − 2.
Thus, the
change in ocean heat storage with time can be used to calculate the
net radiative imbalance of the Earth (Ellis et al., 1978; Piexoto and Oort, 1992).
For example, quarterly anomalies for
net top of the atmosphere radiation (28) show no statistically measurable
change between 2000 and 2008, which is consistent with the lack of a statistically measurable
change in our estimate for
radiative forcing between 2000 and 2007 (SI Appendix: Section 2.8).
Radiative forcing: A
change in average
net radiation at the top of the troposphere (known as the tropopause) because of a
change in either incoming solar or exiting infrared radiation.
What greenhouse gases do is reduce the outgoing longwave radiation (at fixed T) and the
radiative forcing is a measure of that
net irradiance
change, in this case defined at the tropopause.
Re 416 Bernd Herd — in climate science, for global climate
change, specifically a global (average surface) temperature
change in response to a global (typically average
net tropopause - level after stratospheric adjustment)
radiative forcing (or other heat source — although on Earth those tend not to be so big), where the
radiative forcing may be in units of W / m ^ 2, so that equilibrium climate sensitivity is in K * m ^ 2 / W (it is often expressed as K / doubling CO2 as doubling CO2 has a certain amount of
radiative forcing for given conditions).
The reason why a 1 / S ^ 2 prior is noninformative is that estimates of climate sensitivity depend on comparing
changes in temperature with
changes in -LCB- forcing minus the Earth's
net radiative balance (or its proxy, ocean heat uptake)-RCB-.
Natural or anthropogenic CO2 in the atmosphere induces a «
radiative forcing» ΔF, defined by IPCC (2001: ch.6.1) asa
change in
net (down minus up) radiant - energy flux at the tropopause in response to a perturbation.
The forcing is calculated as the perturbation to the
net radiative flux at the tropopause following a model
change such as increased greenhouse gas concentration.
In all cases, however, the
net radiative forcing
changes for the non-CO2 gases are small after 2100 and negligible after about 2200.
The «forcing» by the way is just a measure of how the
net radiative balance of the planet is perturbed by a
change in solar irradiance, greenhouse gases, etc..
Looking at the last decade, it is clear that the observed rate of
change of upper ocean heat content is a little slower than previously (and below linear extrapolations of the pre-2003 model output), and it remains unclear to what extent that is related to a reduction in
net radiative forcing growth (due to the solar cycle, or perhaps larger than expected aerosol forcing growth), or internal variability, model errors, or data processing — arguments have been made for all four, singly and together.
The IPCC defines
radiative forcing as «the
change in
net (down minus up) irradiance (solar plus longwave; in W m — 2) at the tropopause after allowing for stratospheric temperatures to readjust to
radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values».
Radiative Forcing A
change in average
net radiation (in W m - 2) at the top of the troposphere resulting from a
change in either solar or infrared radiation due to a
change in atmospheric greenhouse gases concentrations; perturbance in the balance between incoming solar radiation and outgoing infrared radiation.