Global warming is a fact. Figure (1) plots the average change in Global,
Northern hemisphere and Southern hemisphere temperatures from 1880 to 2018 (reference). The temperature has been rising, more so in the Northern
Hemisphere.
The standard economic story is that global warming
increases the cost of production of food and primary commodities, reduces their
supplies, and as demand keeps rising, the price of commodities increases
(excess demand).[1]
Figure (2) plots the ANZ bank, New Zealand’s commodity price index and
the World commodity price index (it includes meat, skins and wool; dairy;
horticulture, forestry, seafood and aluminium).
Note that both prices increasing as predicted, but the New Zealand
commodity price is often lower than the world’s commodity prices.
Figure (2)
Based on such information, The New Zealand Agricultural
Greenhouse Gas Research Institute concludes, “Climate changes could further
drive up international commodity prices. That in turn would benefit New Zealand
farmers and agricultural exports.”
Figures (1) and (2) clearly imply that the New Zealand commodity price
level (as measured by the commodity price index) is positively correlated with
global average change in temperature (both rising). This is also true for the price of every
commodity in the index (meat, dairy...etc.). However, the conclusion of the
Institute is misguided because the demand for New Zealand’s commodities
depends, not on the New Zealand commodity price alone, but on both, the New
Zealand price and the world’s price.
How is that?
What matters for the demand on the New Zealand primary commodities is
not the New Zaland commodity price per se, but rather the relative
price that is the ratio of the New Zealand commodity price to the world’s
price of the same commodities.
Figure (3) plots the data from Jan 1986 to Mar 2019. The correlation is
negative.
Figure (3)
In a global commodity market, a change in the nominal price of a NZ
commodity exerts two effects on the quantity demanded of New Zealand primary
commodities. First, it changes the relative price, which is a change in
the terms at which a global buyer can exchange a NZ commodity for another
non-NZ commodity (e.g., New Zealand’s dairy and the other countries dairy). The
change in the relative price leads to a substitution effect. A lower
relative price increases global demand for New Zealand’s commodities. Second,
there is an income effect. A change in the nominal price of New Zealand’s
commodity causes a change in real income of the buyers, or in the size
of the basket of primary goods, a global buyer can buy. If global warming
causes the price of a New Zealand commodity to fall, all other prices
remained unchanged, the consumer’s real income rises because more of such good,
or other goods, could be purchased.
Assuming that everything else remains unchanged, the patterns depicted
in figure (2) remain as such under global warming, the higher the New Zealand’s
productivity (in primary commodities sector) is, the lower our relative
commodity prices, and the higher the global demand on our commodities.
Furthermore, although commodity prices are highly volatile, they still
share significant cyclical fluctuations with nominal GDP. They are also
positively correlated with expected inflation. I showed that changes in relative
commodity prices fully explain the Kiwi dollar depreciation rate Razzak, 2018. Global warming is very
relevant to economic policy; see Rudebusch 2019 (here).
Global warming is clearly a danger and a game changer. The economic analyses I have seen so far are thin. Policymakers need a more general equilibrium analysis to understand the costs and the benefits. There must be some benefits, I do not know what they might be. I can imagine that truism might benefit from warmer temperature. Farmers might be able to produce new varieties that they could not produce before, hence opening new markets.
[1] Google for example, How Climate Change
Will Alter Our Food; How Climate Change May Affect Global Food Demand and
Supply In the Long Run; and Roundtable II: Economic Growth and Climate Change:
Long Run Implications for Commodity Prices and Trade.