Solar surface radiation and its impact on measured recent temperature increase in De Bilt, Netherlands

Solar surface Radiation and Temperature Trends:

• Between 2001 and 2020, we explored the hypothesis that the measured increase in solar surface radiation might explain the observed temperature rise at 2 meters above ground in De Bilt.
• To investigate this, we combined solar surface radiation and temperature data from the Royal Netherlands Meteorological Institute (KNMI) with satellite measurements of radiation and cloud cover at the top of the atmosphere from the CERES satellite.
• By analyzing the energy and radiation balance of the atmosphere and considering partial balances at both the surface and the top of the atmosphere, we established connections between the components.
• The study solved for surface temperature, solar radiation reflection fraction, and solar radiation absorption fraction using balance equations.
• Energy balance calibration involved:
• Adjusting the temperature difference between the surface and the 2-meter height temperature to match observed temperature differences.
• Tuning the balance-calculated ratio of total forcing differences to temperature differences (ΔΣFi/ΔT) per season to align with the derivative of the Stefan-Boltzmann radiation law (R^2: 0.9992).
• Interestingly, we found that the atmosphere’s near surface emissivity could be well approximated by a power function of season dependent cloud cover.
• Additionally, the reflection and absorption fractions of solar radiation strongly correlated with cloud cover (R^2 > 0.90).

Key findings and best estimates related to solar surface radiation and its impact on temperature trends in De Bilt, Netherlands, over the period from 2001 to 2020 at a 95% confidence interval:

Surface Warming Contributions:

• Approximately 74% [43-100] of the surface warming is attributed to an increase in solar surface radiation.
• The remaining 26% [0-56] results from an increase in downward thermal radiation  from the atmosphere near the surface.
• No contribution from downward thermal radiation cannot be ruled out.

Atmospheric Warming at 2 Meters Height:

• The warming of the atmosphere at 2 meters height is influenced by several factors:
• Reduced reflection at the top of the atmosphere, contribution 39% [-2-80].
• Increased upward thermal radiation, contribution 29% [6-52].
• Enhanced latent heat and convection, contribution 28% [-6-63].
• Notably, the strong correlation between reflection fraction and cloud cover suggests that the surface-level atmospheric warming is also influenced by decreasing cloud cover.

Discussion about the Energy and Radiation Balance Analysis:

• Unmeasured variables can be inferred from balance equations.
• Observed warming can be explained by changes in energy and radiation components.
• Due to the high variability of the yearly data, the propagation of errors leads to high confidence intervals indicating that the true contribution could plausibly range anywhere from small negative to nearly the complete warming considered.

In summary, Energy and Radiation Balance Analysis indicates that the solar surface radiation  significantly impacts (> 43%) recent warming trends in De Bilt.