The new report said “stronger or different” government action was needed to tackle more than 30 climate-related risks in the next few years, including over coastal flooding, public water supplies and health.
The government’s UK Climate Change Risk Assessment also said it would cost billions every year to deal with the impacts of the climate emergency by the mid-century.
“We have clear evidence demonstrating the pace of warming in recent decades and the impacts we will face should this continue,” the report - published on Monday - said.
“As we redouble our efforts to achieve net zero, we must also continue to raise ambitions on adaptation to ensure the UK is resilient to the challenges of a warming world.”
The report laid out how even a small shift in the average climate can lead to “major changes in extreme events”, including increasing the frequency of severe flooding event, and said preparations needed to be made for the possibility of a 4C rise in temperatures.
The Climate Change Committee (CCC), which advises the government, identified eight priority areas which require the most urgent action over the next two years.
These included the health risk of warmer temperatures in buildings, the impact on people and the economy of a power system failure linked to the climate, and the threat of a supply chain collapse linked to the crisis.
More action was needed over the next five years to protect the UK from 34 potential impacts of the climate emergency, such as damage from flooding, threats to wildlife and people taking ill from rising temperatures.
The risk assessment was published on the same day Office for National Statistics analysis found the climate crisis was already having a negative impact on health in the UK - and this was expected to get worse over time.
The new government report said it recognised the scale of the challenge posed by the climate crisis, but added: “We must go much further and faster to truly prepare for the impacts of a warmer world.”
Baroness Brown of Cambridge from the CCC’s adaptation committee said: “Building resilience to a cocktail of climate impacts facing our country, including flooding, drought, heat exposure and extreme weather events, is a mammoth task and we’re falling well behind.”
She added: “We look forward to seeing the government’s action plan to shift the dial and deliver a well-adapted UK.”
Last year, England’s Environment Agency warned the climate crisis - which leads to heavier rainfall and rising sea levels - was worsening the risk of floods across the UK.
Earlier this month, the climate emergency was named as the biggest global risk by the World Economic Forum (WEF).