Editing IPCC:AR6/WGI/Chapter-10 (section)

=== Interplay Between Human Influence and Internal Variability at Regional Scales ===

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'''Human influence has been a major driver of regional mean temperature change since 1950 in many sub-continental regions of the world''' ( ''virtually certain'' ''').''' Regional-scale detection and attribution studies as well as observed emergence analysis provide ''robust evidence'' supporting the dominant contribution of human influence to regional temperature changes over multi-decadal periods. {10.4.1, 10.4.3}

'''While human influence has contributed to multi-decadal mean precipitation changes in several regions, internal variability can delay emergence of the anthropogenic signal in long-term precipitation changes in many land regions''' ( ''high confidence'' ''').''' Multiple attribution approaches, including optimal fingerprinting, grid-point detection, pattern recognition and dynamical adjustment methods, as well as multi-model, single-forcing large ensembles and multi-centennial paleoclimate records, support the contribution of human influence to several regional multi-decadal mean precipitation changes ( ''high confidence'' ). At regional scale, internal variability is stronger and uncertainties in observations, models and human influence are all larger than at the global scale, precluding a robust assessment of the relative contributions of greenhouse gases, stratospheric ozone, different aerosol species and land-use/land-cover changes. Multiple lines of evidence, combining multi-model ensemble global projections with those coming from SMILEs, show that internal variability is largely contributing to the delayed or absent emergence of the anthropogenic signal in long-term regional mean precipitation changes ( ''high confidence'' ). {10.4.1, 10.4.2, 10.4.3, 10.6.3, 10.6.4}

'''Various mechanisms operating at different time scales can modify the amplitude of the regional-scale response of temperature, and both the amplitude and sign of the response of precipitation, to human influence''' ( ''high confidence'' ''').''' These mechanisms include non-linear temperature, precipitation and soil moisture feedbacks, slow and fast responses of sea surface temperature patterns and atmospheric circulation changes to increasing greenhouse gases. {10.4.3}

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