Lord Krebs sits on an independent panel which advises central government and the devolved administrations on greenhouse gas emissions.
Agriculture is the biggest emitter of greenhouse gases in Northern Ireland, accounting for 29%.
He said flooding was the biggest risk, with about 60,000 homes vulnerable.
Lord Krebs, who was in Belfast to present a report on the specific challenges for Northern Ireland, said increased rainfall could also pose a risk to agriculture from soil erosion.
If properly managed, however, climate change could present opportunities, with warmer summers and longer growing seasons, he added.
Agriculture, power generation and transport are the biggest emitters here.
There have been calls for local climate change legislation; Northern Ireland is the only devolved administration not to have it.
It would mean targets for cuts to greenhouse gas emissions.
But there has been opposition to that, with claims it could make industry and farming here less competitive.
Lord Krebs said climate change could no longer be denied and there was now "absolutely overwhelming scientific consensus" about it.
DUP MP Sammy Wilson said the assembly should not pander "to mostly well off green zealots" by introducing a "disastrous" policy.
Agriculture and Environment Minister Michelle McIlveen has said she would keep the issue of local legislation "under review".

Ann Grisman, from Hereford, disappeared after arriving in Wellington by taxi on 28 November.
The body was discovered by a member of the public on a building site at Longforth Farm, on the outskirts of Wellington, at about 09:30 GMT.
Police said Mrs Grisman's death was not at this stage being treated as suspicious and her family had been informed.
Northern Ireland needs to act now to prepare for the effects of climate change, a senior government adviser has warned.
[NEXT_CONCEPT]
Police searching for a missing 80-year-old woman have found a body.