This study documents the impacts of climate change on firm-level productivity by matching a globally comparable and standardized survey of nonagricultural firms covering 154 countries with climate data. The findings show that the overall effects of rising temperatures on productivity are negative but nonlinear and uneven across climate zones. Firms in hotter zones experience steeper losses with increases in temperature. A 1 degree Celsius increase from the typical wet-bulb temperature levels in the hottest climate zone (25.7 degrees Celsius and above) results in a productivity decline of about 20.8 percent compared to firms in the coldest climate zone. The effects vary not only based on the temperature zones within which firms are located, but also on other factors such as firm size, industry classification, income group, and region. Large firms, firms in manufacturing, and those in low-income countries and hotter climate zones tend to experience the biggest productivity losses. The uneven impacts, with firms in already hotter regions and low-income countries experiencing steeper losses in productivity, suggest that climate change is reinforcing global income inequality. If the trends in global warming are not reversed over the coming decades, there is a heightened risk of widening inequality across countries. The implications are especially dire for the poorest countries in the hottest regions.