The number of undernourished people around the globe increased to nearly 821 million in 2017, the third straight year of growth and the highest figure since 2009, according to a new report from the UN's Food and Agriculture Organization.

Expand chart Adapted from Food and Agriculture Organization of the United Nations, "The State of Food Security and Nutrition in the World"; Chart: Axios Visuals

Why it matters: Along with conflict and instability, this rise in global hunger is driven increasingly by climate change and related extreme weather events, putting some of the world's most vulnerable citizens at even greater risk.

Food insecurity was found to be significantly worse in countries where people are dependent on agriculture for their livelihood, especially when they don't have systems in place to counter the effects of climate shocks.

"It is shocking that, after a prolonged decline, this is the third consecutive year of rising hunger. The inescapable fact is that climate change is now leaving people around the world without enough to eat," Robin Willoughby, head of food and climate policy at Oxfam GB, told The Guardian.

The big picture: Climate change has the potential to erode the gains made toward fighting global hunger over the past decade — which were largely due to political stability, economic growth and greater social protections in the developing world — as extreme weather kicks off more and more societal crises around the world. Some specific weather trends are triggering the worst climate shocks on food stores:

Higher temperatures — and spikes in temperature anomalies — can affect crop yields.

Severe droughts and floods linked to climate change have both seen an uptick in recent years — most notably, flood-related disasters spiked 65% in the last quarter-century.

Changes in seasonality, especially in the developing world, throw off rainfall patterns and growing seasons.

Of the 51 countries that faced food crises in 2017, 34 had climate shocks, per the UN report. The food security threat deepened in the 14 countries that simultaneously faced conflict and regional instability in addition to climate shocks.

Yemen, where 22 million out of 27 million citizens are in need of humanitarian assistance, perhaps best represents this horror. Already one of the world's poorest countries, Yemen faces the combination of an ongoing civil war and serious famine that led UN Ambassador Nikki Haley to remark "no one should ever have to live the way the people of Yemen are living."

The bottom line: Without significant action to address climate change, some of the world's most vulnerable citizens may face increasing risk from global hunger, which was on a marked downward trend just 5 years ago — and the UN had hoped to eliminate fully by 2030.

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