A sweeping United Nations-sponsored review of climate science published Monday projected that the world will cross a crucial temperature threshold as early as 2030 — up to a decade sooner than previously thought.

Why it matters: Warming is affecting every area of the globe, the report notes, and extreme weather events are becoming more common and severe contributing to a more volatile world.

What they're saying:

United Kingdom: "Today’s report makes for sobering reading, and it is clear that the next decade is going to be pivotal to securing the future of our planet. We know what must be done to limit global warming – consign coal to history and shift to clean energy sources, protect nature and provide climate finance for countries on the frontline," U.K. Prime Minister Boris Johnson said in a statement.

• The U.K. hosts the 2021 United Nations Climate Change Conference, also known as the COP26 summit, in November.

United States: “The IPCC report underscores the overwhelming urgency of this moment. The world must come together before the ability to limit global warming to 1.5 degrees Celsius is out of reach," U.S. special climate envoy John Kerry said in a statement.

• "As the IPCC makes plain, the impacts of the climate crisis, from extreme heat to wildfires to intense rainfall and flooding, will only continue to intensify unless we choose another course for ourselves and generations to come."

Activists: "The new IPCC report contains no real surprises. It confirms what we already know from thousands previous studies and reports - that we are in an emergency. It’s a solid (but cautious) summary of the current best available science," Greta Thunberg tweeted.

• "Today, I, and so many other young people, wake up enraged — the IPCC report is apocalyptic, catastrophic, and nothing we haven’t been screaming from the rooftops for years. Our politicians shouldn’t need a report to tell them how bad things are. We’re already living it," Varshini Prakash, executive director of Sunrise Movement, said in a statement.

This story will be updated with more reactions.