The most accurate value of total solar irradiance during the 2008 solar minimum period is 1360.8 ± 0.5 W m−2 according to measurements from the Total Irradiance Monitor (TIM) on NASA's Solar ...Radiation and Climate Experiment (SORCE) and a series of new radiometric laboratory tests. This value is significantly lower than the canonical value of 1365.4 ± 1.3 W m−2 established in the 1990s, which energy balance calculations and climate models currently use. Scattered light is a primary cause of the higher irradiance values measured by the earlier generation of solar radiometers in which the precision aperture defining the measured solar beam is located behind a larger, view‐limiting aperture. In the TIM, the opposite order of these apertures precludes this spurious signal by limiting the light entering the instrument. We assess the accuracy and stability of irradiance measurements made since 1978 and the implications of instrument uncertainties and instabilities for climate research in comparison with the new TIM data. TIM's lower solar irradiance value is not a change in the Sun's output, whose variations it detects with stability comparable or superior to prior measurements; instead, its significance is in advancing the capability of monitoring solar irradiance variations on climate‐relevant time scales and in improving estimates of Earth energy balance, which the Sun initiates.
To distinguish between simultaneous natural and anthropogenic impacts on surface temperature, regionally as well as globally, we perform a robust multivariate analysis using the best available ...estimates of each together with the observed surface temperature record from 1889 to 2006. The results enable us to compare, for the first time from observations, the geographical distributions of responses to individual influences consistent with their global impacts. We find a response to solar forcing quite different from that reported in several papers published recently in this journal, and zonally averaged responses to both natural and anthropogenic forcings that differ distinctly from those indicated by the Intergovernmental Panel on Climate Change, whose conclusions depended on model simulations. Anthropogenic warming estimated directly from the historical observations is more pronounced between 45°S and 50°N than at higher latitudes whereas the model‐simulated trends have minimum values in the tropics and increase steadily from 30 to 70°N.
Reliable forecasts of climate change in the immediate future are difficult, especially on regional scales, where natural climate variations may amplify or mitigate anthropogenic warming in ways that ...numerical models capture poorly. By decomposing recent observed surface temperatures into components associated with ENSO, volcanic and solar activity, and anthropogenic influences, we anticipate global and regional changes in the next two decades. From 2009 to 2014, projected rises in anthropogenic influences and solar irradiance will increase global surface temperature 0.15 ± 0.03°C, at a rate 50% greater than predicted by IPCC. But as a result of declining solar activity in the subsequent five years, average temperature in 2019 is only 0.03 ± 0.01°C warmer than in 2014. This lack of overall warming is analogous to the period from 2002 to 2008 when decreasing solar irradiance also countered much of the anthropogenic warming. We further illustrate how a major volcanic eruption and a super ENSO would modify our global and regional temperature projections.
The beginning of the 21st century has been widely designated a “global warming hiatus” or “pause” or “slowdown” because the rate of change of global surface temperature is a factor of two to three ...smaller than in the last half of the twentieth century. Indeed, observed global surface temperature (shown as black symbols in the top panel) warmed minimally. The rate of change of global surface temperature (shown as black symbols in the second panel) reached its lowest value in the 12‐year interval centered on 2007–2008. But while the terminology “hiatus” and “pause” may imply a reduction or cessation of the warming of the Earth by increasing concentrations of greenhouse gases, statistical models constructed from the observations over two different time periods (the space era, 1979 to 2017, shown as orange lines and the historical era, 1882 to 2017, shown as the blue lines) readily reproduce the observed surface temperature anomalies as simply the mitigation of ongoing anthropogenic warming by natural influences. The bottom panels show that the rates of change in temperature anomalies due to El Niño and La Niña (third panel) and solar irradiance (fifth panel), in particular, have negative values during the “pause” which counter much of the positive anthropogenic influence (sixth panel). Even though natural influences mitigated the anthropogenic warming globally, this was typically not the case regionally. On the right are the different spatial patterns of surface temperature rates of change that the space‐era statistical model attributes to each influence.
Climate change detection and attribution have proven unexpectedly challenging during the 21st century. Earth’s global surface temperature increased less rapidly from 2000 to 2015 than during the last half of the 20th century, even though greenhouse gas concentrations continued to increase. A probable explanation is the mitigation of anthropogenic warming by La Niña cooling and declining solar irradiance. Physical climate models overestimated recent global warming because they did not generate the observed phase of La Niña cooling and may also have underestimated cooling by declining solar irradiance. Ongoing scientific investigations continue to seek alternative explanations to account for the divergence of simulated and observed climate change in the early 21st century, which IPCC termed a “global warming hiatus.” Amplified by media commentary, the suggestions by these studies that “missing” mechanisms may be influencing climate exacerbates confusion among policy makers, the public and other stakeholders about the causes and reality of modern climate change.
Understanding and communicating the causes of climate change in the next 20 years may be equally challenging. Predictions of the modulation of projected anthropogenic warming by natural processes have limited skill. The rapid warming at the end of 2015, for example, is not a resumption of anthropogenic warming but rather an amplification of ongoing warming by El Niño. Furthermore, emerging feedbacks and tipping points precipitated by, for example, melting summer Arctic sea ice may alter Earth’s global temperature in ways that even the most sophisticated physical climate models do not yet replicate.
This article is categorized under:
Paleoclimates and Current Trends > Climate Forcing
Abstract
What drives the small total solar irradiance (TSI) changes of ∼50–100 parts per million (compared with >1000 ppm solar-cycle amplitudes) during a deep solar minimum, i.e., in the practical ...absence of detectable sunspots and long-lasting active regions? We consider the epoch 2008 June–October and investigate multiple data sets (TSI; various Mg
ii
line-activity indices, extreme ultraviolet fluxes, and full-disk magnetograms) to show that variations in TSI closely follow changes in total magnetic flux from sources with ∣
B
∣ > 80 G (up to ∼600 G) that persist even during extended periods with no detectable sunspots. These sources comprise the populations of (a) short-lived (<20 minutes), small-scale (predominantly a single 2″ MDI pixel), ∼evenly distributed regions, and (b) on average, more extended (a few MDI pixels) and longer-lived (140–260 minutes median lifetimes) magnetic areas. We ascribe the latter to ephemeral regions, finding them clustering on ∼200 Mm scales. We speculate that the short-lived MDI sources are linked to the ubiquitous magnetic bright points. Our analysis of magnetic flux variations during solar cycle 23 shows that the magnetic regions present during this deep solar minimum elevate the total magnetic flux above the total flux in just the Gaussian “cores,” fitted to histogram distributions of the full-disk flux. This suggests that solar irradiance during more extended, even deeper minima, such as the Maunder Minimum, may be lower than in 2008.
Because of the dependence of the Sun's irradiance on solar activity, reductions from contemporary levels are expected during the seventeenth century Maunder Minimum. New reconstructions of spectral ...irradiance are developed since 1600 with absolute scales traceable to space‐based observations. The long‐term variations track the envelope of group sunspot numbers and have amplitudes consistent with the range of Ca II brightness in Sun‐like stars. Estimated increases since 1675 are 0.7%, 0.2% and 0.07% in broad ultraviolet, visible/near infrared and infrared spectral bands, with a total irradiance increase of 0.2%.
How Does the Sun’s Spectrum Vary? Lean, Judith L.; Deland, Matthew T.
Journal of climate,
04/2012, Letnik:
25, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Recent observations made by the Spectral Irradiance Monitor (SIM) on the Solar Radiation and Climate Experiment (SORCE) spacecraft suggest that the Sun’s visible and infrared spectral irradiance ...increased from 2004 to 2008, even as the total solar irradiance measured simultaneously by SORCE’s Total Irradiance Monitor (TIM) decreased. At the same time, solar ultraviolet (UV) irradiance decreased 3–10 times more than expected from prior observations and model calculations of the known effects of sunspot and facular solar features. Analysis of the SIM spectral irradiance observations during the solar minimum epoch of 2008, when solar activity was essentially invariant, exposes trends in the SIM observations relative to both total solar irradiance and solar activity that are unlikely to be solar in origin. The authors suggest that the SIM’s radically different solar variability characterization is a consequence of undetected instrument sensitivity drifts, not true solar spectrum changes. It is thus doubtful that simulations of climate and atmospheric change using SIM measurements are indicative of real terrestrial behavior.
Abstract
Statistical models that account for the separate influences on total atmospheric ozone of ozone-depleting substances, anthropogenic greenhouse gases, and natural processes are formulated ...from the Merged Ozone Data (MOD V8 and V8.6) and used to explore scenarios for ozone’s evolution from 1900 to 2100. The statistical models based on MOD V8 project larger growth in total ozone during the twenty-first century than do coupled chemistry–climate models globally and in the tropics where the chemistry–climate models indicate persistent ozone depletion. The statistical models based on MOD V8.6 suggest, instead, that total ozone everywhere never (or barely) recovers to 1980 levels. Since the decline in ozone-depleting substances and the increase in greenhouse gas concentrations are both expected to increase ozone in the twenty-first century, these results suggest that downward instrumental drifts may be present in MOD V8.6. Instrumental drifts, of opposite sign, may also be present in MOD V8 since it is possible to reduce the projections of the corresponding statistical models to agree with those of the chemistry–climate models by altering the long-term trends of the MOD V8 data within the estimated long-term uncertainty. Alternatively, the chemistry–climate models may project excess tropical ozone depletion by overestimating trends in the upwelling of tropical (ozone poor) air associated with global warming and the resultant decline in mean age of air. This possibility is consistent with independent observations that the age of stratospheric air has not declined during the past three decades, as the globe has warmed 0.3°C, and that model parameterizations of tropical convection may be inadequate.
The LASCO Coronal Brightness Index Battams, Karl; Howard, Russell A.; Dennison, Hillary A. ...
Solar physics,
02/2020, Letnik:
295, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present the construction of a new white-light coronal brightness index (CBI) from the entire archive of observations recorded by the
Large Angle Spectrometric Coronagraph
(LASCO) C2 camera between ...1996 and 2017, comprising two full solar cycles. We reduce all fully calibrated daily C2 observations of the white-light corona into a single daily coronal brightness observation for every day of observation recorded by the instrument, with mean daily brightness values binned into 0.1
R
⊙
radial
×
1
degree angular regions from 2.4 – 6.2
R
⊙
for a full 360 degrees. As a demonstration of the utility of the CBI, we construct a new solar irradiance proxy that correlates well with a variety of direct solar irradiance observations, with correlations shown to be in the range of 0.77 – 0.89. We also present a correlation mapping technique to show how irradiance correlations depend on, and relate to, coronal structure/locations, and to demonstrate how the LASCO CBI can be used to perform long-term “spatial correlation” studies to investigate relationships between the solar corona and any arbitrary concurrent geophysical index. Using this technique we find possible relationships between coronal brightness and plasma temperature, interplanetary magnetic field magnitude and (very weakly) proton density.
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