[M-AG32] Renewable Energy

[MAG32-05] Factors controlling low-frequency changes in near-surface wind speed

*Ingo Richter¹ (1.JAMSTEC Japan Agency for Marine-Earth Science and Technology)

Keywords:climate change, natural variability, near-surface wind speed, terrestrial stilling, wind power

Observations indicate that near-surface wind speed over land has been declining from about 1980-2010, a phenomenon known as terrestrial stilling. This is thought to be due to increasing greenhouse gas concentrations, which stabilize the atmosphere. A continuation of this trend would have serious implications for wind energy generation because the energy that can be generated by wind turbines scales with the third power of wind speed and is therefore sensitive to even small changes. Recent observations, however, suggest a recovery from terrestrial stilling, with a strong upward trend from 2010-2017. This has been attributed to multi-decadal modes of climate variability, such as the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Variability (AMV). Natural variability patterns, such as PDO and AMV, oscillate about the mean state and average out to zero. Greenhouse gas forcing, on the other hand, leads to long term changes that do not reverse sign in the foreseeable future. It is therefore crucial to determine whether the wind speed fluctuations since 1980 are due to natural variability or anthropogenic forcing.
Here, we examine climate model output from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to evaluate the relative importance of climate change and natural variability on near-surface wind speed fluctuations. Model simulations with steady radiative forcing (experiment piControl) show that natural modes of climate variability do have an impact on wind speed over land, but that this impact is far too weak to explain the observed reversal in terrestrial stilling from 2010-2017. Changes of terrestrial wind speed under observed radiative forcing (experiment historical), on the other hand, are roughly consistent with the observed stilling from 1980-2010, though also weaker. This suggests that natural climate variability cannot be the main reason for the recent reversal in terrestrial stilling. Alternatively, it suggests that climate models fail to adequately represent the impact of natural variability on near-surface wind speed.