How much could an “intelligent community” living outside our cosmic neighbourhood deduce by a preliminary scan of our solar system?
After observations for a few orbits of the inner planets, the most interesting from a change perspective would surely be the third one, residing in the “Goldilocks zone”, that region not too close or far from the central sun.
From space, the most obvious features of Planet Earth, as now can be seen from in the above images from the Living Earth application (http://www.livingearthapp.com)
* the meridian separating night from day:
* the extensive blueness of the Pacific Ocean that covers almost a hemisphere without housing any major landmass;
* the North and South poles whose sparkling white ice cover and mountains form quite separate worlds;
* the Third pole, that mass of ice and snow that covers the Tibetan plateau and surrounding regions, and
* the great red deserts of Australia and Africa.
Also visible are the glaciated mountains of the Andes, the Alps, Urals and the Rockies, and the glimpses of ice in the tropical areas of South America, Africa and West Papua.
Ice and oceans cover nearly 75% of the globe.
During the day, the equatorial forests of the Amazon and West Africa offer evidence of living matter. At night, everything changes and the lights of Europe, North America and the coastlines of most continents emphasise the straight-line geometries caused by mankind. Equatorial and polar regions are now the dark zones of the world.
Anyone watching the full electromagnetic spectrum of the earth over the entire orbit around its sun would be struck by how the tilt of the earth’s axis gave rise to a waxing and waning of ice cover over the poles and by the irregular passage of the monsoonal fronts in alternate hemispheres. Seasonal effects also show up in the blooming of the chlorophyll signatures in the oceans, the greening and browning of grasslands in the sub-tropics, the movement of the equatorial storms and the changing extent of the ozone holes over the poles.
Differences between the two polar regions would be intriguing; less variability in ice-cover at the southern pole would imply a continental underlying structure. The current downward trends in late-summer ice-cover would suggest mainly sea-ice and an increasing interaction with more tropical waters via large-scale currents in the Atlantic Ocean. Many indicators would suggest the presence of layers in both the atmosphere and oceans – and of interactions between them.
Patterns of activity
At regular intervals, the display of aurora lights simultaneously over both polar regions would confirm an atmosphere responding to sun emissions entering the outer magnetic zone (ionosphere) expected of dense planets. Observations of the earth’s rim of atmosphere would note electrical discharges from large thunderstorms and the presence of dust and other light-absorbing pollutants in the lower atmosphere. Absorption bands (dips in the intensity of light at characteristic frequencies) in the spectra of the atmosphere would be an obvious indicator of complex life-forms in the oceans or on land. Lightning activity would be noted as concentrated in major-bands of clouds near the equator, especially in Central Africa. This suggests a strong vertical movement in the layer of air closest to the surface (the troposphere); the spreading cloud-tops would herald a transition to the next vertical layer (the stratosphere).
Major volcanic eruptions would be visible from afar; the rapid movement of dust around the relevant hemisphere would suggest strong zonal winds in the stratosphere. This dust moves more slowly across the equator and may not reach the poles, implying some zonal structure through much of the atmosphere.
Over a few earth rotations, many cloud systems in the troposphere retain their spiral structure and pass in succession within narrow bands of latitude, usually disintegrating within 16-18 days from birth – the so-called synoptic systems. On occasions, these cloud systems protrude towards the equator and seem to be slowed down. The synoptic system is impeded and extreme weather can now pass more easily along the meridians, the lines of longitude connecting the two poles.
A more persistent observer could not fail to marvel how ocean upwellings and downwellings, as exhibited by ocean texture and cloud patterns, change in strength and location over 4-7 orbit periods. They would note how sudden shifts over 1-2 orbits appear in the position of the equatorial rainfall and vegetation. They might ponder why the irregular 20-30 year cycles in ocean reflectance and the tantalizing 60 year and longer cycles in air and ocean temperatures lead to correlations of weather characteristics between quite distant parts of the globe.
Planet Earth is a amazing set of intricate images with strongly-varying spatial patterns over different timescales; it is a complex and adaptive system if ever there was one in this part of the universe. An advanced civilisation would send orbiting satellites of their own as remote-sensing probes of the structure of the atmosphere, the patterns of winds, and the detailed signatures expected from a breathing and seething planet.
Gravity sensors would weigh the ice-caps and note their changes in thickness over time; the gravity waves in the atmosphere would give a good indication of the major perturbing mountain-scapes across the globe.
The poles would be obvious places to drill long-core samples of ice. These samples would be analysed for historical dust and gas content, radioactivity levels (for dating the different slices of ice) and for any sophisticated correlations needed to construct a full climate history back to the time of deposition of bedrock ice cover. Surprises would be in store as the time histories from different ice-fields would show strong and coherent oscillations in time and between different sampling points. The earth’s atmosphere would become more easily understood in terms of a few basic patterns, especially in the last 20,000 years as the climate departs from the regular succession of ice ages that dominated the earth╒s history for the previous million years.
As intelligent beings, their community would be very keen to approach such an interesting planet and see for itself what type of living organisms dominate the land-use, oceans and climate. They would ask whether the oceans possess similar complex structures as the atmosphere. Do the lower and upper atmospheres interact with each other in a significant way and are the energy and matter fluxes with the oceans dominated by exchanges at their interface? How did life form and how is this linked to its changing climate? What has caused the very recent and major changes in the composition of the atmosphere and the patterns of weather obvious in the limited time of observations? How will all these changes accelerate and what next equilibrium will be formed? Will the Earth remain in a stable regime or are major perturbations about to sweep across the globe? Will such changes be along latitudinal zones or along meridians linking the poles? Should they concentrate on the poles or tropics to monitor the important symptoms?
Views from the earth
In many ways, we earth-bound observers are very much blinkered by our history of observations, initially by personal senses and then by dedicated instrumentation. Meteorological measurements of a scientific nature only started in the eighteenth century in European locations. The temperature history of Central England goes back to 1736. Measurements for many European and North American cities started in the mid-nineteenth century. The navies of the world were some of the first regular observers and today we are reaping the benefit of regularly-timed observations taken along the ship paths of exploratory and regular shipping routes.
Tropical and polar observations really began in the late nineteenth century and were fairly sparse until after the first world war. Regular measurements of the three-dimensional structure of the atmosphere had to await the satellite era; ocean measurements only became comprehensive in the last decade as the set of Argo multi-sensor workhorses have scanned the deep structure of the upper ocean. Surface weather observations have been limited to around 200 years, and mainly in major western countries. Nevertheless, a long-term view of three-hourly information across the globe is now made possible by using historical measurements within trusted forecasting models to yield detailed weather reconstructions of varying reliability.
We can now ask how major weather events such as hurricanes, drought and heat-waves have varied over the past 140-200 years, what patterns of activity are evident and whether the extreme events that affect everyday lives and livelihoods are changing in frequency, intensity and location.
To look further back in time, we can supplement our ice core samples from the poles with those from tropical glaciers that adorn equatorial mountains, and also look at the variations in tree rings, coral deposits, lake sediments and other proxies for seasonal weather changes. The synthesis now taking place suggests that many surprises lie in store. Such analyses show that the three poles, the oceans and the equatorial zone dominate the world’s weather and climate. There are other factors. In the scheme of things, sea-ice plays a surprisingly important role in how weather events and seasonal changes occur throughout the world. The other sleeping giants are the mid-level and deep ocean currents that transport the sun’s heat across the globe; the chemistry of the upper atmosphere involved in keeping out the harmful ultraviolet radiation; and the influence of natural and man-made dust emissions.
The importance of changing patterns in the atmospheric and ocean circulations is most apparent in the frequency of extreme events in many regions, as explained in this recent ABC report
and the Nature series at