Out of balance in the Arctic

Polar bears have high energy requirements that rise further as a result of climate change As human activities lead to rising greenhouse gas concentrations in Earth's atmosphere, less incoming solar energy is released back into space, causing a net energy gain that increases global temperatures. The consequence of climate change for polar bears can likewise be understood in terms of an energy imbalance. Sea ice melting reduces the opportunities for polar bears to capture seals (see the photo), leaving them at risk of expending more energy in the pursuit of food than they can obtain. The magnitude of this imbalance is determined by their rate of energy use. On page 568 of this issue, Pagano et al. ( 1 ) quantify the energy expense of wild polar bears and show that it is higher than previously estimated.