The rise and flaws of systematic reviews on climate change effects

Oral
2024 Prague [Global Evidence Summit]
Alonso P1, Ávila-Oliver C2, Grigorios L3, Kappes M2, Morgan R4, Nahuelhual P5, Neumann I2, Piggott T3, Queñelen E5, Schünemann H6
1Iberoamerican Cochrane Center, Hospital de Sant Pau, Barcelona, España
2Universidad San Sebastián, Santiago, Chile
3Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada
4School of Medicine, Case Western Reserve University, Cleveland, Ohio, United States
5Unidad de Evaluación de Tecnologías Sanitarias, Ministerio de Salud de Chile, Santiago, Chile
6Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada; School of Medicine, Humanitas University, Milan, Italy

Background:

The impact of climate change on human health is a pressing global concern. Developing robust and tailored methods for synthesizing evidence is essential for accurately assessing its impact.

Objectives:

We aimed to describe and analyze the methodologies and reporting practices of systematic reviews (SRs) that provided quantitative estimates of climate exposures on health outcomes.

Methods:

We conducted a comprehensive search for systematic reviews that quantified the impact of climate exposures on health outcomes in MEDLINE and EMBASE. Two reviewers independently screened the identified studies. Data extraction was performed using standardized forms.

Results:

A total of 37 SRs with meta-analysis were identified, showing a steady increase in number since 2012. Most reviews included time series analyses. The most frequently reported outcomes were mortality and morbidity due to extreme weather events. The methodologies used in conducting and reporting these SRs were highly variable. A critical assessment of the primary study limitations (risk of bias) was performed in only 24 (65%) of the reviews. Moreover, only seven (19%) of the SRs evaluated the certainty of the evidence, with six of them applying the Navigation Guide framework and one using a modified version of the GRADE approach. In all these cases, the certainty of evidence assessment relied on concepts now considered outdated (eg, assigning a “low” level of certainty of the evidence to observational studies of exposures).

Conclusions:

The number of systematic reviews addressing the effect of climate change on health outcomes is increasing. However, many of these reviews lack robust and structured methodologies and depend on outdated conceptual frameworks. These findings highlight a critical need for more rigorous and updated approaches in this field.