The ongoing emission of greenhouse gases is triggering changes in many climate hazards that can impact humanity. We found traceable evidence for 467 pathways in which human health, water, food, economy, infrastructure, and security have been recently impacted by climate hazards such as warming, heatwaves, precipitation, drought, floods, fires, storms, sea level rise, and changes in natural land cover and ocean chemistry. By 2100, the world's population will be exposed concurrently to the equivalent of the largest magnitude in one of these hazards if greenhouse gasses are aggressively reduced or three if they are not, with some tropical coastal areas facing up to six hazards concurrently. These findings highlight that greenhouse gas emissions pose a broad threat to humanity by simultaneously intensifying many hazards that have been harmful to numerous aspects of human life.Ongoing greenhouse gas emissions are simultaneously shifting many elements of Earth's climate beyond thresholds that can impact humanity 1 . By affecting the balance between incoming solar radiation and outgoing infrared radiation, man-made greenhouse gases are increasing the Earth's energy budget ultimately leading to warming 1 . Given interconnected physics, warming can affect other aspects of the Earth's climate system 2 . For instance, by enhancing water evaporation and increasing the air's capacity to hold moisture, warming can lead to drought in commonly dry places, in turn ripening conditions for wildfires and heatwaves when heat transfer from water evaporation ceases. There are opposite responses in commonly humid places where constant evaporation leads to more precipitation, which is commonly followed by floods due to soil saturation. The oceans have the added effect of sea warming, which enhances evaporation and wind speeds, intensifying downpours and the strength of storms, whose surges can be aggravated by sea level rise resulting from the larger volume occupied by warmed water molecules and melting land ice. Other inter-related changes in the ocean include acidification as CO2 mixes with water to form carbonic acid, and reduced oxygen due to warming reducing oxygen solubility and affecting circulation patterns and the mixing of surface waters rich in oxygen with deeper oxygen-poor water. These climate hazards and their impacts on human societies occur naturally but are being nontrivially intensified by man-made greenhouse gas emissions, as demonstrated by an active research on detection and attribution (discussed under Caveats in the Methods section). With few exceptions 3 , changes in these hazards have been studied in isolation whereas impact assessments have commonly focused on specific aspects of human life. Unfortunately, the failure to integrate available information most likely underestimates the impacts of climate change because i) one hazard may be important in one place but not another, ii) strong CO2 reductions may curb some but not all hazards (See Fig. S1), and iii) not all aspects of human systems are equally challenge...

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Groundwater elevations in coastal cities will be affected by climate-change-induced sea level rise (SLR) and wastewater collection systems will experience increased groundwater infiltration (GWI) due to greater submergence of sewer pipes. Commercial sewer hydraulics models consider GWI to be a constant quantity estimated via a low-flow monitoring campaign and are incapable of predicting future flows due to changes in GW elevations. A global sensitivity analyses conducted for a two-dimensional GWI pipe flow model found the most important input parameters are groundwater head and surrounding soil hydraulic conductivity. Two case studies were conducted considering a range of pipe defect severity to estimate increases in GWI associated with predictions of future SLR. The findings are that SLR will begin to have noticeable impacts in terms of increased average dry weather flow (ADWF) as soon as 2030 (3–10%) and will increase dramatically in the future (10–29% by 2050, and 50% or more by 2100). Daily and seasonal tide ranges affect the normal diurnal flow variations by between 3% and 10%. The estimation methodology and case studies described here illustrate the coming future importance of SLR effects on GWI in coastal collection systems that should be included in facilities planning and design.