The first month on Cat Ba Island – getting my bearings

My apologies for the long gap between posts, life has been a bit busy.

I recently began a new position in Vietnam, on Cat Ba Island to be specific.  My first impressions are that this is a damp and precipitous landscape.  I have not seen the sun since I arrived in Vietnam on March 4th.  For Cat Ba Island this means a riotous profusion of greenery tempered by the steep terrain and lack of soil.

Where the northern end of the road terminates

Where the northern end of the road terminates

This is a land where Ymir’s bones lie close to the surface, broken and weathered, their calcium leaking back into the waters from which these precipitous cliffs rise.  The geology is the first thing that strikes you here.  The cliffs have been weathered by millions of years of rain, the ever-so-slightly acid rainwater eating into the ancient limestone creating a mature karst landscape.  Like bones, coral, and seashells, limestone is primarily made up of calcium carbonate, which in other forms makes marble and dolomite.  This is probably one of the reasons this is a place where snail diversity is immense, ranging from tiny frilled creatures more akin to limpets to giant land snails, many of which are still unknown to science.  Snails need lots of calcium to make their shells.

Unknown frill terrestrial snail

Unknown frilly terrestrial snail

Land snail shells collected around the office - and a wasp nest

Land snail shells collected around the office – and a wasp nest

The banded limestone found here is a relic of abundant diatom (a type of plankton) skeletons laid down five hundred million yeas ago and subjected to the vagaries of time.  Limestone, while soft to the chisel and hammer, is a remarkably durable stone at the macro-scale, one of the reasons climbers like it, but at a chemical level it is easily weathered.  We are often told that water has a pH of 7, that is it neutral.  Natural rainwater, we then assume, should also have a pH of 7, but it is closer to 5.6 due to the dissolution of carbon dioxide into the water making carbonic acid.  A pH of 5.6 is about as acidic as a cucumber or an onion for comparison.  Of course, other environmental factors can reduce this tremendously, leading to extremely acidic rain.  Rain falling on the limestone erodes small channels in the rock that look like thumbprints in wet clay.

Rainwater erosion on limestone

Rainwater erosion on limestone

Eventually these concentrate water flow, carving small holes in the stone reducing it to a swiss-cheese like structure with an extremely jagged and sharp exposed surface.  These little caves connect into larger caves.  In these protected, damp environments bacteria grow, exuding waste products and creating hydrogen sulfide that mixes with the water and makes a weak sulfuric acid, increasing the chemical weathering.  This cycle persists, eventually leading to enormous caves.

The airflow in these caves evaporates the mineral rich water tricking through the now porous stone and the calcium carbonate re-solidifies into stalagmites, stalactites, soda straws, and any number of strangely beautiful and complex cave structures.

Caves often form in weak portions of the stone and, eventually, gravity takes its toll and the weakened rocks collapse leaving behind steep spires and fields of slowly eroding boulders.

Limestone spi

Limestone spire in the north end of Cat Ba Island

Cat Ba and Ha Long Bay are examples of a drowned karst landscape, a mature karst landscape that has been flooded by rising waters.  What little soil does form is washed down into the many bays, coves, and channels of the region, leaving little for plants to sink roots into.  In the shallow waters of the bays mangroves find nutrients, in abundance.  Here mangroves are near the northern margin of their range, their numbers restricted and the trees short, making low dense forests.

Gray mangroves on the south western side of the island

Gray mangroves (Avicennia marina) on the south western side of the island

As in many places, the mangroves are in trouble here, often cut down to make shrimp farms.  This leads to reduction in local fisheries, increased erosion, and lack of protection from storm surges and tsunamis.  The local government is taking steps to protect what remains and to, potentially, restore some of the previous mangrove forests.  In the rich mud of the mangrove regions there are numerous animals, among them one of my favorites, mudskippers, amphibious fish that hop about in the mud protecting their little territories.

Mudskipper amongst mangrove roots

Mudskipper amongst mangrove roots

On the cliffs however there are few nutrients and plants grow in what cracks and declivities they can find.  As per many islands there are a number of endemic species, here one of the most commonly seen ones is the Ha Long Cycad (Cycas tropophylla), an ancient type of gymnosperm that looks like a cross between a fern and a palm tree.

Ha Long Cycad (Cycas tropophylla), endemic to a 400km square area, globally rare, locally abundant

Ha Long Cycad (Cycas tropophylla), endemic to a 400 square km area, globally rare, locally abundant

The season here is shifting into spring and some of the trees have begun blooming, among them the hoa gạo or Cotton Tree (Bombax ceiba), so named for the kapok-like fibers that are found in the seed pod.

Hoa Gạo (Bombax ceiba), Cotton Tree in English.  The Vietnamese name translates to "Rice Flower"

Hoa Gạo (Bombax ceiba), Cotton Tree in English. The Vietnamese name translates to “Rice Flower”

 

I still have not seen the little primates I came here to work with, they are few in number and they clamber about on the vertical cliffs like, well, monkeys.

Soon though.

Tides, Why Tide Charts Don’t Average to Zero, and Agendas

Tides are an important part of life on earth. Earthly tides are primarily governed by the moon, a result of Lunar gravity tugging on the planet as the Earth spins along side of our over-sized neighbor.

A few days after the 2013 "supermoon"

A few days after the 2013 “supermoon”

Tides affect both the earth’s crust (raising it enough so that large particle accelerators must be designed with the geo-tide in mind) and, more familiarly, the oceans. Technically speaking, all bodies of water are affected by the tides, but the large tides experienced by coastal dwellers is a result not only of the Earth-Moon-Sun gravitational dynamic but of resonance, coastline shape, and of characteristics of the ocean floor.

Resonance is simply the self-reinforcing effect of synchronization. The most familiar form of resonance for most people may be pumping your legs on a swing. If your timing is right the small amount of energy added to the pendulum motion by pumping your legs will lift you higher and higher. If your timing is off you can kill your speed and come to a stop. You can do the same with your hand and a basin of water, a small amount of hand motion will quickly wind up sloshing water out of a bathtub. Swings, tides, and lasers work on this principle of resonance.

The shape of the coastline and the depth of the ocean floor can concentrate or diffuse tides as well, focusing or dispersing the vast energies at play. This is why the tides in places with fjords like British Columbia and Norway can be so dangerous.

I grew up near the ocean and spent a lot of time watching the ocean and exploring tidepools and the rocky beaches of the California coast.

Mussels anchored on exposed rocks in the intertidal zone.

Mussels anchored on exposed rocks in the intertidal zone.

The interesting part of the coast was not the sandy beaches, but the craggy high surface areas that trapped pools of water. All sorts of creatures live in these pools. Strange and wonderful creatures like the Gumboot Chiton, Cryptochiton stelleri, large molluscs that crawl out of the water at low tide to feed on exposed seaweed.

Cryptochiton stelleri, or Stellars's Hidden Chiton, so named because the characteristic eight bony plates are hidden under rugose red skin

Cryptochiton stelleri, or Stellars’s Hidden Chiton, so named because the characteristic eight bony plates are hidden under rugose red skin

In tidepools I have found and caught octopus, eels, and fish, but two of the most common residents are Shore Crabs

Shore Crab, a common California coast resident

Shore Crab missing an arm, a common California coast resident

and anemones, both hovering between the scavenger and hunter niches.

Anemones: close-up of arms

Anemone: close-up of arms

These and many other creatures live in what is known as the intertidal zone, the region of the coast that is above low tide and below high tide. This is an area of tremendous free energy. Energy is a two edged sword as any scientist or engineer can attest to. Energy makes all things possible, and most things can be broken down into either growth or destruction. Creatures that live in the intertidal zone reap the benefit of straddling two environments, feasting on the windfall of both, but the fierce waves and tides also expose them to the dangers of being left to suffocate in water, desiccate in the sun, be torn from holdfasts, and fall prey to other adaptable creatures. Excellent potential for great growth or swift destruction.

In the intertidal zone there are bands of life that roughly conform to the amount of time spent out of water. Mussels and barnacles occupy the upper reaches and are the most familiar.

Mussels and Gooseneck Barnacles on exposed rocks.  Both are tasty to eat.  Mussels are commonly eaten in the US and Gooseneck Barnacles fetch high prices in Spain, where people risk their lives to collect them.

Mussels and Gooseneck Barnacles on exposed rocks. Both are tasty to eat. Mussels are commonly eaten in the US and Gooseneck Barnacles fetch high prices in Spain, where people risk their lives to collect them.

Lower down, in some places, Sea Palm grows in dense stands, often damaged by the waves.

Sea Palm (Postelsia palmaeformis), the only species of this kelp and one of the few that can live for extended times out of water

Sea Palm (Postelsia palmaeformis), the only species of this kelp and one of the few that can live for extended times out of water

At each level a different selection of species dominates creating a many-layered composite of ecotones, much like a mountain in miniature. The vertical ranges for these species collections is so narrow that it can be used to track sea level changes.

If you want to see nudibranchs, octopus, and sandcastle worm, then when do you go to the coast?

sandcastle worm (Phragmatopoma californica) colony

Sandcastle Worm (Phragmatopoma californica) colony

Clearly you go at low tide… but what does this mean?

One of the things that bothered me about tide-charts (like the one below) is that if you average the high and low tides you do not get zero.

Graphical tide chart made with the TideTrac app

Graphical tide chart made with the TideTrac app

I went out a while back to experiment with day-time long exposure photos. This is the tide chart for the day. Notice that the lowest tide of the day is still +0.4 feet (12cm)? The average tide for the day is +2.9 feet, nearly a meter. What is that all about?

The answer is that tide charts were designed for sailors, not tide-poolers or surfers. Tide charts are set by a datum, one of 17 potential datums, that all are based off of the LOWEST tides, not the average tide. For a sailor who wants his boat to stay in the water and not be slammed against rocks, this is important.

Even a small bump carries a lot of energy

Even a small bump carries a lot of energy

For the rest of us, it is a little non-intuitive. We have picked the lowest tide as the datum because that is what was important to the people making the charts at the time. If it had been house contractors instead, the datum would have been the highest tides. Tide-poolers would probably have picked the average tide as the datum, making it easy to determine when the most species would be exposed at any given moment.

There is a lesson here; be wary of maps and charts. Maps and charts are made to tell a specific story, a story with a perspective, a message, and an agenda. Like an advertisement on TV or a political speech, it is important to be aware of both the audience and the proponents of the product. And in truth, there is little that is more political than maps and charts.

Oh, the long exposure photos turned out great.

Ten seconds of waves washing in and out during the day

Ten seconds of waves washing in and out during the day

***

Note: for those of you who look at the full-sized photos, several of these have been pulled from my archives and were taken with my first digital camera; a Canon ELPH from the early 2000s. A great little camera, but of a disappointingly low resolution.

A Long Flight over the Canadian Shield

Recently I flew from Istanbul to Los Angeles, following a great-circle route over Ukraine, Norway, Greenland, and Northern Canada.  As I always do when flying, I got a window seat and spent most of the flight peering out the window, developing a crick in my neck that took several days to loosen.

Much of the European and Greenland portions of the flight were shrouded in clouds, leaving me watching a vast expanse of what looked like glowing cotton.  Occasionally patches would open in the clouds and I would catch a brief glimpse of the land or sea below, and a look at one of the most talked about ecosystems on our planet.

Ice floes on the Arctic Ocean

Ice floes on the Arctic Ocean

The northern polar region, the Arctic.  This is a vast region centered on the bath-tub-like basin of the Arctic Ocean.  Discussing directions in the polar regions is tricky, for in the arctic, pretty much every direction that is not north is south, thus geography is a better indication of location than compass points.  On one side the entryway to the Arctic Ocean is narrow, shallow, and flows over the ancient land-bridge that once connected North America and Asia.  On the other side warm water flows up the Atlantic Ocean to the east of Greenland, keeping Europe warm and pushing the ice away from the Norwegian coast.  This is the primary point of water-flow into the Arctic Ocean.

To the west of Greenland a network of channels in the Queen Elizabeth Islands lets water slowly filter out of the basin, trickling back into the Atlantic via the southern opening of Baffin Bay.  Amongst the islands fierce currents keep polynyas open in the ice, providing open water for eider ducks and other sea-birds that over-winter in the Arctic.  Generally the whales will leave the Arctic during winter, but sometimes they become trapped and these polynyas provide the only places they can find air to breath.

Since we have been keeping records the sea ice extent has been getting smaller and smaller.  Records of sea ice extent and other cold-weather data can be found free of charge at the National Snow and Ice Data Center.

Several years ago, as part of a graduate project on Ringed Seals I looked at the changes in ice extent for the month of April over the last 30 years.  The photo of the broken sea ice above was taken on the eastern side of Greenland, a place where the sea-ice is extremely variable.

1981 - 2010 April Sea Ice Extent:  Darker colors indicate a greater number of years of coverage, lighter colors, fewer years of coverage

1981 – 2010 April Sea Ice Extent: Darker colors indicate a greater number of years of coverage, lighter colors, fewer years of coverage – green indicates areas outside of ice-cover that are shallow enough to provide foraging areas for Ringed Seals

The little flashes of ice I got to see through the grubby Turkish Airlines plane window were tantalizing, but they were only teases.  The interesting views were to come later, as we passed over the Canadian Shield.

Flying over over the Melville Peninsula, looking east to Foxe Basin... I think

Flying over over the Melville Peninsula, looking east to Foxe Basin… I think

Here, over the Canadian Shield, a 3 million square mile (8 million square kilometer) expanse of heavily weathered, exposed bedrock billions of years old the signs of past glaciation are evident.  Not merely evident, the fossil tracks of vast continental glaciers shout their presence to the sky.  Fortunately, I happened to be in the sky, with a camera at the ready.

There is a common misconception about glaciers.  People have heard that glaciers carve channels into the bedrock and grind down mountains.  This is only partially true.  Ice is not very hard, by itself ice can carve channels into rock the hardness of chalk or talc, but not into tough rocks like granite, the rock much of the Canadian Shield is composed of.  Ice levers out whole boulders and picks up loose material where it lies.  These become embedded in the ice and these are what does the scouring and carving.  The ice provides the weight and movement, much like a person provides the force when sanding or filing a piece of wood or metal, but it is the sandpaper or the file that does the actual cutting.

Ice, when it comes in glacier quantities, is an elasto-plastic material.  The upper surfaces are brittle and crack, making crevasses and seracs, but the deeper ice, down below the 50 meter mark, is more akin to a slow, cold silly-putty than to the brittle thing we put in lemonade.  When the ice is kilometers deep it oozes, flowing like spilled molasses over the land, dragging with it the entrained materials, grinding down high points, smoothing jagged surfaces, and hollowing out U-shaped valleys, leaving behind a stream-lined surface replete with the marks of its passage.

Rocky Mountain Trench in the Canadian Rockies - a classic glacially carved valley

Rocky Mountain Trench in the Canadian Rockies – a classic glacially carved valley

In both photos above the U-shaped valleys are clear.  These valleys come in all sizes, some more impressive than others.  The Rocky Mountain Trench in British Columbia is one of the more impressive ones, as is the Gilkey Trench in South-East Alaska.

The Gilkey Trench, the speck in the foreground is a person and each of the ripples in the bottom is 10 meters high

The Gilkey Trench, the speck in the foreground is a person and each of the ripples in the bottom is 10 meters high

These valleys are often found in mountains, places where the glaciers ground out material between the peaks, but left the high places alone.

Billions of years ago the Canadian Shield used to be home to vast mountains, now they are all gone, only their roots remain.  Erosion from various sources and repeated glaciations have scoured the Canadian Shield over and over again, grinding even the great mountains into low mounds, leaving traces that are best seen from the air.

Exposed bedrock showing fault-lines and ancient mountain cores

Exposed bedrock showing fault-lines and ancient mountain cores

The long, straight lines are old fault lines, places where geologic stresses broke the rock and let it slide against itself.  Here the rock is already damaged and the glaciers excavated long channels that look like canals from the air.  The distorted oval in the lower middle of the photo is where a bubble of rock forced its way up in the distant past, creating a mountain or large hill.  Now it has been ground flat and shows up in the surface pattern, much like cut wood shows the pattern of knots and grain despite being smooth to the touch.

Over much of the Canadian Shield soils are shallow to non-existent.  Even south of the tree-line vast areas are sparsely vegetated for lack of soil.  Roads are difficult to make as the land is smooth only at large scale and it is riddled with lakes and rivers.

In the winter the smoothest parts of the Canadian Shield are the lakes themselves and they are where temporary roads are made.

A road on the frozen lakes to the north of Yellowknife

A road on the frozen lakes to the north of Yellowknife

The last major glaciation was relatively recent, only about 20,000 years ago and the land is still recovering from the effects.  The whole Canadian Shield is undergoing isostatic rebound; with the weight of the up to 3 miles (almost 5 kilometers) of ice coming off the Earth’s crust it is now rising, seeking a new equilibrium as it floats on the liquid rock mantle deep beneath the surface.  Rivers and lakes are draining, the courses sometimes shifting as the land rises, carving out new pathways.  Water, like the ice it came from, does not do the work of carving the rock, it is the sediment it carries, but the Canadian Shield is made of hard stuff and it takes time to carve new channels in this durable granite.

Meandering rivers in glacial sediment

Meandering rivers in glacial sediment

Further south, the land is still flat, but has been overlain by a layer of sediment, left behind as the glaciers retreated.  Here rivers carve into the land more easily, looping back and forth and pinching off sections of themselves.  These oxbow lakes and the irregular rocky ones to the north are home to untold numbers of mosquitoes and other insects with aquatic life-phases.  These insects, when they emerge, lure birds from as far away as the southern hemisphere, and the mosquitoes become the bane of any humans wandering in the vastness of northern Canada during the warm season.  These insects, both adult and larval provide feed for numerous fish, making this an excellent place for fishing.  The first time my family and I drove to Alaska much of our food was from fish we caught each evening after only a few minutes with a line in the water.

The glaciers that covered the Canadian Shield were continental in scale.  There are only a few places where vast sheets of ice like that remain, but many places (for now) where small alpine glaciers are present, and even more places where signs of past glaciation are common.

One of the most famous of the post-glacial relics is Half Dome in the Sierra Nevada mountains of California.

Half Dome

Half Dome

The last interesting views I had out the window of my plane were of Half Dome, or Tis-sa-ack in the local native language.  This sheer rock-face is a batholith, a granite upwelling often making the core of a mountain.  Despite its appearance, Half Dome was not split in half, it seems to have formed more or less in the shape it has now.  Glaciers have smoothed and rounded the upper surface and carved out the characteristic U-shaped valley below though.

Glaciers have had a far larger impact on the world than most people realize.  Humans reached Australia some 60,000 years ago, able to walk over-land all the way to where Bali is now, needing boats only for a short stretch from Bali to Lubok.  Fifteen thousand years ago people walked from Siberia to Alaska over a broad grassy plain when the sea level was some 300 feet (91 meters) lower than today as a result of the water locked up in the ice.

When Greenland and Antarctica melt (which they will eventually do with or without our presence, the only difference is when it happens) sea level will rise by some 200 feet (67 meters) above present day levels.  At the moment there is a lot of talk of halting climate change via geo-engineering projects.  This is talk that completely and painfully misses the point.

The climate is a dynamic system, one that experiences wide changes over long periods of time, with the changes sometimes happening rapidly.  Yes, we desperately need to stop messing with the climate by releasing fossil CO2, methane, CFCs, and all the other greenhouse gasses we pump into the atmosphere with such abandon.  We are pushing the natural changes hard, forcing them to be of greater magnitude and to happen faster than they would otherwise.  We need to stop this, but what we do not need to and should not do is compound our mistakes by dumping iron into the oceans, pumping sulfur into the upper atmosphere, or place orbiting mirrors in space to deflect sunlight in a misguided attempt to keep the climate the way it was during the early 1900s.

We are driven by our economic system to keep things in some idealized stasis based on the time when we built our current infrastructure.  We may want things to stay static, but the earth is dynamic and fluid.  In our short-sighted, profit driven efforts to “save” our political and economic systems we will destroy the very thing that those systems and our societies are based on.

Seeing the earth from new perspectives and thinking about what we see tells us about the world is important.  We are on a cusp, we are standing on the edge of our metaphorical Half Dome.  We can tumble off the steep edge with disastrous consequences, or we can ease our way back down the slightly less steep slope, and once more enjoy the rich valley floor below.

Happy Aphelion! Wait, what’s that and how does it relate to the climate?

Well, today is one of the most interesting days of the year for me.  This year, 2012, July 5th is aphelion, the day that Earth is furthest from the sun in its orbit.

It is rare (in the tens of thousands of years scale) that the northern hemisphere summer solstice are so close to aphelion.

The time during the year that aphelion and perihelion (when we are closet to the sun) changes over a roughly 100,000 year cycle, known as the Milankovitch Cycle.  Our orbit around the sun is not a circle, it is an ellipse with an eccentricity of about 0.0167.  This orbit both changes shape and rotates around the sun much like a spirogram tracing out a flower-like shape.

Ellipse with 0.5 eccentricity. Earth has a much smaller eccentricity, making the orbit more nearly, but not exactly a circle. Aphelion and perihelion are the two ends of the egg shape.

Perihelion precession

 

It is summer in the northern hemisphere, a time when people often say things like, “We are closer to the sun than we are in winter.”  This is not really true.  Summer is a product of the angle at which Earth is tilted, right now Earth is tilted so that the northern regions lean toward the sun.  In terms of orbit we are actually at the furthest point Earth gets from the sun.

This has interesting implications in terms of the global climate.  This means that right now winters tend to be warm (the planet is closer to the sun) and summers cool (the planet further from the sun).  In the big picture this places us in the midst of a global cool cycle, the type of situation that tends to lead to ice ages, like the one we are emerging from.

The climate picture is not so simple, though.  Even in terms of celestial mechanics there are other factors that play into the climate picture.  Two large, cyclical factors are the precession and wobble of the Earth. One of these is the obliquity, or the angle at which Earth is tilted.  This is our Axial Tilt, and it is currently 23.4º, but the Axial Tilt changes between approximately 22º and 24º, over a 41,000 year cycle.  This affects where the tropics lie and how much solar energy different regions of Earth receive.

Range of Axial tilt – Wikipedia indicates 22.1º to 24.5º , other sources vary on the exact outer limits of the range, but they are all near 22º and 24º of tilt.

The final large scale cycle that comes into play is Axial Precession.  Spin a top, or a gyroscope; the handle by which it was spun precesses, or rotates around the axis of spin at a fixed angle.  In the case of Earth this cycle varies between 19,000 and 23,000 years.

Precession – just like a top or gyroscope, Earth’s axis of spin makes a slow circle

No single one of these factors leads to an ice age or global tropical forests, they must combine in just the right way to set the conditions.  These cycles are like waves in water, sometimes they cancel each other out, other times they reinforce each other.  Past climate records show clear evidence of the effects of these cycles.

NASA – Orbital Time Series showing the cyclic nature of the three major orbital cycles

NASA – Solar Insolation (energy received from the sun) and O18 (an heavy isotope of oxygen) records in sediment indicating temperatures at the time the O18 precipitated.  O18 is heavier, so it takes more energy to keep it aloft, and water made from this isotope tends to precipitate first when the temperature drops.

Once the orbital conditions are right then, other Earth surface factors come into play.  Where mountain ranges are, whether oceans are polar or tropical, how saline the oceans are, the arrangement and distribution of the continents , and volcanic activity, such as the Deccan and Siberian Trap.  These are immense lave flows in India and Siberia that pumped immense amount of greenhouse gasses into the atmosphere and seem to have strongly affected the climate.  Even short duration, one-off events such as the 1815 eruption of Tambora in the Dutch East Indies (now Indonesia), can have global climate effects.  Tambora is implicated in what is commonly known as The Year Without Summer when the global temperatures dropped by 0.4–0.7 °C , leading to massive famines across the northern hemisphere as  result of immense crop shortages.  This may have been a period of low solar activity as well, adding to the poor growing conditions.

Impacting bodies also can play a major role in the global climate.

The upshot of this is that we really should be paying close attention to the current rapid warming trend as it is happening at a time when it appears, from the large scale cycles, that conditions are not right for a warming trend of the magnitude we are experiencing.  This is a warning sign, one that we need to pay attention to.

The climate always changes, and that is as it should be.  The problem we now face is that our physical and social infrastructure has been built around the idea that the changes are small and seasonal rather than global and systemic.  Our cities, roads, fields, power generating systems, and economies are based on things pretty much staying as they are, which will not happen.  Even without us tipping the scale the climate would not stay the same.  We need to be aware of this and act accordingly, looking at the much larger picture.

If we don’t, well, life on Earth will be just fine in a few tens of millions of years, but we may not be around to see it.  If we continue on the path we are now taking, we many not even be around to see the northern summer occur at perihelion.

This is our planet.  Right now it is the only one we have.  Understand it, enjoy it, and please don’t break it.

The good folks at NASA have put together a great, short paleoclimate primer at the link below, which is where the last two charts come from.

http://earthobservatory.nasa.gov/Features/Paleoclimatology_Evidence/

The first three images from from the Wikipedia article on Milankovitch Cycles – they had the best diagrams.

I will return to the usual, smaller scale aspects of nature in the next post, which will be about Dogbane.