Up to a point, projected climate change is not all bad news in that respect.
There are some positive effects in terms of extending the growing seasons and ranges of some plants and improving growth rates.
"The negatives are increasing temperatures to the point where there would be increased droughts on the east coast, increased rainfall on the west coast, increased storm events and increased biosecurity risks [of incursions of pests and diseases]," says Mr Hodgson.
Over time the net effect gets more and more negative, he says. "And it gets added to - though there is a lag here - by an increase in sea level, which, when coupled with dry conditions on the east coast, will result in salt water movement under the land and soil salinity, especially in the Canterbury and Heretaunga plains."
All of that is over the next 100 years and at the middle of the range of the temperature rises projected by the Inter-governmental Panel on Climate Change, the United Nations body which has the job of distilling a consensus view from the world's climate scientists for the benefit of policymakers.
"At the rate we are going, those things will happen anyway because Kyoto has got a 'too little, too late' feel about it. But it is a start," Mr Hodgson says.
Business opponents of ratification point to the modest environmental gains from Kyoto's first commitment period (2008 to 2012) to argue that the costs would be disproportionate.
Full compliance with Kyoto would only mean that the world will reach six years later whatever temperature it would otherwise have reached by 2100.
If Kyoto is an insurance policy, they say, not only are the premiums too expensive, but the excess or damage incurred before the policy has any effect is way too high.
The pro-Kyoto response is that it is only the first stage of an ongoing process. If the scientific consensus continues to move in the same direction, the agreement will hopefully become more comprehensive and set more stringent emission reduction targets for later commitment periods.
The Business Roundtable, for one, is not convinced that adjustment and adaptation to a changed climate might not be the cheaper option.
In its submission to a Government consultation document on Kyoto, the Roundtable says that land use and husbandry practices in agriculture are constantly adjusting. "It seems unlikely moderate climate change would pose particular problems for the sector or for related issues such as water supply."
Roundtable economist Dr Bryce Wilkinson says New Zealanders as a whole might be better off with a moderate degree of global warming.
Winter illnesses are a greater source of absenteeism from work and pressure on public hospitals than summer illnesses, and more people die from cold than heat.
"We need a proper, dispassionate analysis of why, if it is moderate warming, New Zealanders wouldn't regard themselves as well pleased."
Mr Hodgson's other main argument for ratifying is that under Kyoto, New Zealand as a whole is quids in.
This is because it is allowed to offset growth in emissions of greenhouse gases by credits for the carbon dioxide taken out of the atmosphere by trees in "Kyoto" forests (those planted since 1990 on land not already forested).
Pine trees will be extracting greenhouse gases from the atmosphere faster than cattle, cars and smokestacks are adding them.
Under Kyoto, New Zealand would undertake the target of getting its net emissions of greenhouse gases back to 1990 levels on average between 2008 and 2012.
It can be pretty confident of meeting that target. The projections are that on a business-as-usual basis, with no Government action at all, New Zealand is likely to be emitting 13 to 15 million tonnes of COinf2 more each year than it did in 1990.
But the "sink credits" for the COinf2 taken up by Kyoto forests are likely to be in the order of 20 to 22 million tonnes a year.
With more in the credit than the debit side of the Kyoto ledger, New Zealand is in a fortunate position, says Mr Hodgson. "We earn more than we spend, what's the problem?" Given that, and our reliance on an equable climate, whether to ratify Kyoto is a no-brainer, he says. .
The hard decisions are about how, when and to what extent people are exposed to the "carbon price".
That is the international price of tradeable rights to emit greenhouse gases, akin to fishing quota. They are the units with which Kyoto countries will have to square accounts under the agreement.
In theory, the price should reflect the marginal cost of reducing emissions in a world in which the right to emit is rationed.
Businesses are confronted with two major uncertainties. They don't know what carbon price will be and they don't know to what extent, how or when the Government will transmit the national obligations under Kyoto to individual sectors, firms and ultimately consumers.
Mr Hodgson was not giving too much away on those questions when he talked to the Herald last week.
But he indicated that the forest sink credits, which provide a hedge against the international carbon price, give the Government some leeway over transition and allocation issues.
"We are looking at a staged introduction and ongoing policy reviews. Within two months we will have a preferred policy outline and it will show some quite clear characteristics about what a likely policy framework will be and how it might change over time. Then we will consult on that."
The common thread in business concerns is that they will face costs under Kyoto that competitors in countries outside the pact will not.
Policies which caused production to move from New Zealand to a non-Kyoto country, or which tipped the balance of an investment decision against locating new plant in New Zealand, would do nothing for the global environment and would damage New Zealand's interests to no purpose.
Mr Hodgson acknowledges this: "We need to have policy that gives the appropriate level of assurance that this is not an issue."
Competitiveness can still be eroded by the imposition of some form of carbon charge.
How much of a problem this is depends on the (unknown) price of carbon, and on how sensitive a firm's market share and profitability are to energy and transport costs, compared with other factors.
So what options does the Government have if it wants to ratify yet sees some force in these competitiveness arguments?
"We have some carefully worded cabinet minutes which say it is our intention to distribute 'some proportion' of the sink credits," says Mr Hodgson.
This, then, is the Government's dilemma. It wants to ratify the protocol because it sees global warming as a long-term threat to the primary sector.
But because developing countries, the United States and possibly Australia will be outside the Kyoto agreement for at least the next 10 years, participation would place New Zealand firms at varying degrees of international competitive disadvantage.
However, Kyoto gives New Zealand a hedge against the cost of compliance, in the form of forest sink credits.
It looks as if the Government is wrestling with how to use those credits to ease the transition to a carbon-rationed economy.
Ratification would not commit the Government to distributing the sink credits to the owners of Kyoto forests.
"It does, however, commit us to taking real and measurable steps to address the heart of the problem, which is an over-reliance on fossil fuels and the inefficient use thereof," says Mr Hodgson.
"It is out of the question to ratify and do absolutely nothing and use sink credits to cover emissions and take no action.
"What I must do is keep that balance, come up with policies that concern competitiveness issues - which policies can fall away as other countries come in in later commitment periods."
* In Forum tomorrow, the Pan Industry Group on climate change and the New Zealand Business Council for Sustainable Development have their say on Kyoto.
nzherald.co.nz/climate
Intergovernmental Panel on Climate Change (IPCC)
United Nations Environment Program
World Meteorological Organisation
Framework Convention on Climate Change
Executive summary: Climate change impacts on NZ
IPCC Summary: Climate Change 2001
