The climate niche of Homo Sapiens (2306.00002v1)

Abstract: I propose the Dominicy-Hill-Worton estimator to estimate the current climate niche of Homo Sapiens and our croplands. I use this to extrapolate the degree of unprecedentedness of future climates. Worton's peeled hull is a non-parametric, N-dimensional generalization of order statistics. Dominicy and colleagues show that Hill's estimator of the tail-index can be applied to any homogeneous function of multivariate order statistics. I apply the Dominicy-Hill estimator to transects through Worton's peels. I find a thick tail for low temperatures and a thin tail for high ones. That is, warming is more worrying than cooling. Similarly, wettening is more worrying than drying. Furthermore, temperature changes are more important than changes in precipitation. The results are not affected by income, population density, or time. I replace the Hill estimator by the QQ one and correct it for top-censoring. The qualitative results are unaffected.

• The paper characterizes the climate niche of Homo sapiens using Dominicy-Hill-Worton and peeled convex hull estimators on temperature and precipitation data.
• Key findings indicate humans are more sensitive to temperature increases, with a 60C rise potentially displacing 40% of the population into unprecedented climates, while precipitation changes have minimal impact.
• The study highlights the asymmetric risk posed by warming trends outside the current climate niche, emphasizing the urgent need for climate adaptation and mitigation strategies.

The Climate Niche of Homo Sapiens

The paper "The Climate Niche of Homo Sapiens" by Richard S.J. Tol explores the climatic conditions that are habitable for humans and their croplands within the context of climate change. Utilizing the Dominicy-Hill-Worton estimator, the research aims to characterize the climate niche currently occupied by Homo sapiens, predicting the potential implications of unprecedented future climates. This work applies advanced statistical methods including Worton's peeled convex hull and the Dominicy-Hill estimator to understand human occupancy within climate space, delineated by variables of annual average temperature and precipitation.

Methodological Approach

The paper employs Worton's peeled convex hull, a non-parametric approach, allowing for the estimation of species’ niche by identifying the order statistics in a multidimensional climate space. This is complemented by Dominicy and colleagues' generalization of Hill's estimator to calculate the tail index, assessing the likelihood of encountering climates beyond observed conditions. This combined methodology produces a nuanced analysis of human adaptability to climate extremes. The Hill estimator was replaced by a quantile-quantile (QQ) estimator for robustness and adjusted for top-censoring, establishing qualitative consistency in results.

Key Findings

The statistical analysis reveals differentiated responses to climate extremes with a thick tail distribution at low temperatures and a thin tail at high temperatures. The paper highlights warming and increased precipitation as more concerning than their counterparts. Specifically, a 6°C increase in average temperature could potentially displace 40% of the human population into uncharted climatic territory. Conversely, a 30% change in precipitation would minimally affect the population distribution. The findings suggest a greater sensitivity of humans to temperature increases than to precipitation fluctuations. Importantly, the statistical analysis displayed consistency across various demographic variables such as income and population density.

Implications and Future Research

The paper underscores the asymmetric risk posed by future climate scenarios, particularly warming trends beyond the currently occupied climate niche, posing significant challenges for humankind. The findings challenge prior assertions made by Xu and colleagues, advocating for more efficient statistical models that eliminate biases, such as censoring outliers. The implications of this paper suggest that humanity's adaptive capacity could be strained unless adequate measures are implemented to mitigate climate change impacts.

Future research should integrate additional climatic variables potentially influencing human habitability and adaptive strategies to anticipate more resilient future outcomes. Moreover, the nuanced understanding of croplands' responses to climatic extremes portrays parallel themes, albeit with even thinner tails indicating higher sensitivity.

These findings have significant policy implications, emphasizing the urgent need for multi-faceted approaches to climate adaptation and resilience building to mitigate potential existential threats due to climatic shifts. Enhanced predictive models and robust statistical frameworks continue to be pivotal in climate impact assessment and the development of sustainable ecological and agricultural practices. This research provides a critical lens through which future climatic policies can be evaluated and formulated to ensure human sustainability amidst growing climatic uncertainties.