Trends In Surface Solar Radiation Or Global Dimming And Brightening

Significant multi-year trends in Eg# during the first decades that measurements were made were reported by a few scientists during the twentieth century. Many of these decreasing trends, called 'global dimming' [23], were in excess of 1% per decade. They were viewed with considerable scepticism by the scientific community. The reasons for this scepticism are important because they reflect on the way current science is carried out. Here are some possibilities:

a. Previous texts, which were accepted as foundations of climate science, assumed that earth's solar radiation budget was constant on the short term time scale (i.e. hundreds of years [26]), although changes in solar activity and the solar constant were included as possible drivers for long term (i.e. 103 107 a) climate changes (see Ref. [27] for a review of climate change theories up to the mid 1960s).

b. Climate change science has been dominated by the influence of the ubiquitous and steadily increasing atmospheric greenhouse gases, and especially CO2. A large effort has been made to establish that this change is large enough to warrant worldwide political action. The magnitude of 'global dimming' was clearly of the same order of magnitude as the greenhouse gas influence. If large changes were occurring un-noticed to the scientific community, how good was our understanding of climate and climate change? That question may have been viewed as a threat to the attempts to harness political action and the unprecedented funding that climate change science was receiving [28].

c. Climate change science has focused on TOA influences (e.g. TOA radiative forcing) and assumed that the distribution of energy within the system is less important.

d. Solar radiation is highly variable spatially and temporally and this high variability has hampered integration of worldwide trends. This is in sharp contrast with greenhouse gases which mix well in the atmosphere and whose rate of increase can be discerned within a few years.

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