Hit You Where You Live

Like the majority of people, I live in the northern hemisphere. And like the vast majority of people, I don’t live at sea, I live on land.

NASA GISS, in addition to reporting its global temperature measurements for 2007, also reports monthly data for land areas and for northern-hemisphere (NH) land, and annual data for a number of different latitude bands. Continuing our survey of NASA’s recently released year-end temperature data (still waiting for year-end data from HadCRU and NCDC), let’s take a look at the NASA results for NH land and its various latitude regions, i.e., the place where I (and probably you) live:

For NH land, the three hottest years on record are the last three years: 2007, 2005, and 2006, and last year (2007) was the hottest. NH land areas are warming considerably faster than the globe as a whole. Because the oceans have such a large thermal inertia, land area warms faster. Also, the northern hemisphere has far more land than the southern, so it lacks the strong moderating influence of the southern oceans.

What’s been happening since 1975 (the “modern global warming era”)? Here are the monthly data values (small open circles), annual averages (large filled circles), and a smoothed curve (red line):

While the planet as a whole has been warming since 1975 at 0.018 deg.C/yr, the NH land has warmed at 0.031 deg.C/yr, nearly 70% faster! In fact NH land has warmed more than a full deg.C just since 1975. We can see this more clearly by removing the monthly data points and expanding the y-axis:

Just as warming has been uneven between northern and southern hemispheres, and between land and sea, so too it has been different for various latitude bands covering NH land. The mildest warming (if it can be called “mild”) has been in the lowest latitude band, from the equator to 24N (for latitude bands, NASA reports annual averages but not monthly data):

Since 1975 we have:

Despite it’s “mild” cooling, this latitude band has experienced over 0.7 deg.C warming just since 1975. But the next northerly band, from 24N to 44N, has seen nearly a full deg.C warming:

But there’s more to come as we move further north, to the 44N-64N latitude band, with over a full deg.C since 1975:

Even this dramatic, rapid warming seems mild by comparison to the northernmost region, from latitude 64N to the pole:

This region has seen just about 2 deg.C warming in a mere 33 years. In other words, its present warming rate is close to 6 deg.C/century.

We can plot the smooth versions of temperature change for all four latitide bands on the same graph, to get an idea of how they compare:

This makes it even clearer that as one moves further north, warming become greater. It also emphasizes that the northern cryosphere, especially the north polar ice cap and the Greenland ice sheet, are likely to be profoundly affected. It’s no wonder that native peoples in far northern regions have already noticed substantial changes to their environment, changes which threaten their way of life.

Here are, for NH land and each latitude band, the warming rates from 1975 to the present, the net warming according to the linear warming rate, and the net warming as estimated from the smoothed data:

Land Region	Rate 1975-2008	Net(linear)	Net(smooth)
NH	0.031	1.01	1.11
Equator-24N	0.021	0.70	0.77
24N-44N	0.029	0.95	0.91
44N-64N	0.037	1.24	1.30
64N-90N	0.057	1.87	2.00

Even the most southerly of the NH land regions is experiencing faster warming than the globe as a whole, and the highest latitude band is warming 3 times as fast.

As the temperature difference between land and sea increases, we can expect the moderating influence of the oceans to become more prominent, so over the next century the oceans will retard land warming. On the other hand, we can also expect the atmospheric concentration of greenhouse gases (especially CO2) to keep increasing. So I’ll venture to guess that we shouldn’t expect the NH land warming rates to decrease any time soon (i.e., in our lifetimes).

If the people of the world can find a way dramatically to reduce our emissions of greenhouse gases, then I’ll be happy to be proven wrong. If not, then we’re in for an extremely bumpy ride. Right where we live.