Fingringhoe Wick - intertidal area.

The Colne estuary is well known for attracting large numbers of waders and other water birds. The problem is that its quite large, difficult to watch, and for a visitor with little knowledge of the habitats and tides, its a bit hit and miss.

What would be really useful is a specially excavated wetland that can take large numbers of birds as the tide rises and falls, ideally with a suitable hide with large windows and arm chairs where you can sit in comfort and calmly search through flocks of waders. And, as if by magic, here it is, the newly opened intertidal area at Fingringhoe Wick.

Taken from the EWT twitter feed

A visit on Wednesday on arising tide had spectacular numbers of waders. Rough numbers only but many hundreds of Black-Tailed Godwit, low hundreds of Avocet,  many tens of Dunlin, Ringed Plover, Grey Plover, Knot, Redshank, add in some Bar-Tailed Godwit, Curlew, Oystercatcher, Lapwing, then at least 10 Greenshank, a Common Sandpiper, and well picked out by another birder 2 Curlew Sandpiper, and that's quite a wader list. About 20 Wigeon, some Little Egret, and an obliging Kingfisher made for a cracking list.

The fields by the hide had Meadow Pipit and some common finches, and there were some willow Chiffs hoetting in the bushes. The reserve had lots of hornets around too, so a good visit.

An excellent addition to the list Essex birding sites. I think a return visit may happen in the near future.

Canvey and East Tilbury

So, a scorching September day with a SE wind. Migration mayhem or Summer birding doldrums? I headed to the Thames Estuary to find out, first stop Canvey Point.

A row of empty benches meant I had clearly got this wrong, as at even slightly productive times there are a few locals set up here. I sat and admired the expanse of calm estuary that high-tide had brought. Slowly some birds appeared - a small party of Teal upstream, a few Swallows from over my shoulder, some adult Mediterranean Gulls flying around easily picked out by their plump appearance and translucent primaries. Then a distant Black Tern, juvenile presumably from the darkness of the plumage, flying strongly out then back up the estuary. Most intriguing was a bird the size of a very small skua flying rapidly but gracefully low over the river. Uniform brown, I realised I had no idea what family it belonged to. Eventually it rose up and I could see an extended neck and head so I guess a wader of some description but honestly I have no idea. Moments like that make sea-watching fun.

There were 4 cetaceans mid stream, the curved backs and fins breaking the surface. Eventually one came far enough out to reveal a bullet head - Porpoise. Very nice too. Then a Clouded Yellow over the memorial lawn.

And so on to East Tilbury. It is over a decade since I last went so this was a trip of rediscovery. What a place! Titchwell on my doorstep! Masses of birds round Coalhouse Fort, mainly Starling and House Sparrow but a Blackcap and Willow Warbler, then Stonechat and Linnet on the way to across there grassy area along the sea wall to the estuary. The estuary is hard to watch as the grass hides the near mud, but the tide was falling so soon the mud became exposed a long way out. Some belting Grey Plover made the trip worthwhile just for their sparkling plumage alone. There were Bar-Tailed Godwit, some Knot, and Turnstone with them. A Hobby was hunting behind the sea wall then over the estuary, and a Marsh Harrier came over from Cliffe., and Kestrel and Sparrowhawk gave four raptors in as many minute. An adult Yellow-Legged Gull was feeding on the foreshore. A weasel ran out of the grass then back between my feet.

I walked back and round Coalhouse Fort to the structure due south of the fort. On the way there was juvenile Whinchat, and on the estuary upwards of 800 Avocet that all took off and flew further upstream. Just an awesome sight, the stuff of TV documentaries. A flock of 20 Commic Terns and 2 Sandwich Terns appeared and sat on the mud. Better birders than I would surely have picked up some Arctics but distance, heaths, blah blah. 3 Seals were hauled up on the mud - Common Seals? - Finally as I sat by the estuary I found 2 juvenile Curlew Sandpiper amongst the Dunlin and Ringed Plover and a late Common Swift barrelled over going E down the river.

The whole area was full of insect life too. There was what I am calling "Thames Bee" as I have seen this elsewhere in the estuary - blackish with a narrow white band top and bottom of thorax and a whitish tail. Possibly Shrill Carder but I need to see more of this one to have any idea. There were lots of Wall Butterflies, some Small Heath and a couple of Small Copper, and lots of odanata. I could spend all day here and still be seeing stuff. Expect more!

Blue House Farm and Canvey Point revisited

The Pec was back. An hour away, nice reserve, easy decision. When I got there it was clear a number of others had thought similarly and folks turned up all morning, consequently the hide was well populated but good natured throughout.

The Pec was not visible at first. A wader about 100 yards out looked promising; it was asleep and stood facing away, but a brief lift of the head gave encouragement - not a Snipe. An hour later and it had rotated slightly to show white on the flanks and underneath, and then about thirty minutes later it completed the rotation et Voila! An unbroken neat breast band. Pectoral Sandpiper on the year list.

As is often the case when going see rarities, the star of the show was something different. In this case, a juvenile Curlew Sandpiper. It was consorting with two Ruff and came close under the hide. The three of them stood on a small island and the reflection of them in water as they stood bathed in direct sunlight from behind was something to behold. Needless to say my photo does not do justice.

The chap next to me had some top gear - a prime 500mm lens with a 1.4x converter. He very kindly offered to let me put my camera base on his lens and soon I was clicking away. What a lens! Auto focussing, the lot. There's a couple of cropped photos below. the poor composition is my fault but the crispness of the birds is something to behold. A very generous offer to put thousands of pounds of gear in my hands, the kind of encounter that gives you a warm glow all day.

Hobby hunting over the marsh, adult Yellow Wagtail in front of the hide and 2 Lesser Whitethroat in the car park completed the list.

I had intended to go to East Tilbury on the rising afternoon tide to get waders plus maybe some sea birds on the SE wind, but with the Curlew Sand in the bag I was off to Canvey Point instead. There had been some action in the morning but there was nothing to be seen when I got there. We managed 20 Commic Terns upstream, a Hobby from across the river ended up flying right over our heads, and towards the end of the watch a distant Manx Shearwater was drifting out of the estuary. That just left the local birds to admire; several Mediterranean Gulls, hundreds of Oystercatchers, a small flock of sparkling Grey Plovers, and a few Sandwich Terns. With some excellent company and warm sunshine it was a cracking second part to the day's watching.

BirdGuides has WWBT, Pom Skua, sooty shearwater and several Black Terns in the estuary today, but these birds are generally the reward to locals for many hours watching, and its an achievement to see any of these if you just turn up for a couple of hours on the off chance. Today was just nice to sit in the sun and see what drifted past.

Blue House Farm EWT.

In search of a Pectoral Sandpiper. Needless to say it had gone. Despite this, or perhaps even because of this, a chance to enjoy the current glut of waders and other associated birdlife.

A juvenile Spotted Redshank was the star of the show, with a few Ruff, some Ringed Plover and Little Ringed Plover, Black-Tailed Godwit, 3 Greenshank, Green Sandpiper, Snipe, and Dunlin. Just about all giving good views (see some uncommonly non-rubbish photos by me below!) Otherwise there were several Yellow Wagtails, 4 separate Marsh Harriers, and a few other bits and pieces. Some excellent chat with a couple of reserve managers in the hide too as they discussed the challenges both bureaucratic and environmental of running the reserve. the current crop of waders is partly due to a brief flooding of sea water to help eradicate an invasive Tasmanian plant, so is unlikely to be repeated next year. All the money has historically come from the EU, so there are some challenges in the years ahead to persuade the UK government to continue this work.

A really nice reserve. And what a pleasure to be able to set my scope up in a hide and look through it without having to get into a back-crippling half-squat.

hunting for migrants in an Easterly wind

As the high moves NE, winds whip round the bottom of it in a clockwise direction and straight down the river Thames. Filling the estuary with sea birds.

My instinct is correct. My timing is awful. High tide was 8:30, low tide 2:30. The birds come up on the rising tide, and are nowhere to be seen when I am there at 12 just before low tide. There were Black-Tailed Godwits, a Bar-tailed Godwit, various common waders, some Sandwich Terns squabbling on a sand bank.

I cut my losses and went back via Hanningfield Reservoir to try and get Curlew Sandpiper on my list. Again, lousy timing - I couldn't see them anywhere and wader numbers were down on yesterday. Even so there was a juvenile Black Tern mid reservoir, a Garganey popped its head up at just the right time. There was a Black-tailed Godwit, 3 Dunlin, 4 Ringed Plover, 2 Green Sandpipers, about 8 Common Sandpipers, and 2 Pintails in eclipse. Nothing that looked remotely like a Curlew Sandpiper. sigh.

Thames Estuary Waders

Vange then Rainham.  Lesser Yellowlegs, Spotted Redshank, Ruff, Blackwit, and an accommodating male Bearded Reedling at Vange, Then Temminck's Stint, Little Stint, Wood Sandpiper, Greenshank, Ruff, Blackwit, Snipe, Common Sandpiper at Rainham. All views good but distant.

Here's the Lesser Legs at Vange.

here's a close up to help you find it.

Climate change from the last ice age to the present day

The last ice age ended around 11,000 years ago. The temperature rose by several degrees over a period of around a thousand years to produce a climate we recognise as being similar to our own. Since that time the climate has been roughly constant with some notable periods of variation. Within the time period of recorded history there was a warm period around 0 AD, again from 950-1250 AD (the Medieval Warm Period) and between them cooler periods such as the Little Ice Age (1250-1650). It is instructive to note here that temperature changes are under a degree.

The causes of these events are unclear. There are cycles between ice ages such as the Dansgaard-Oeschger cycle that occurs every 1500 years (called Bond events in the Holcene [1]). This cycle may be oscillatory in nature shuttling heat between the north and southern hemispheres; warmth flows from one hemisphere to the other, causes melting which disrupts flows of warmth between hemispheres, resulting in cooling happening again. The two warm periods noted above only occurred in the northern hemisphere so may have been due to these Bond events.

Solar cycles have been identified as being a forcing event for the climate [2,3,4]. Periods of sun-spot activity have an eleven year cycle and show some correlation with recorded temperature.

When reading about these periodic variations some issues become apparent. Firstly, the temperature changes are small. It is worth noting that an El Nino can raise the global temperature by a few tenths of a degree [5], so these periods are within the natural variation of global temperatures. Secondly the periodic cycles that occur in the sun and earth’s rotation are not set to clockwork and there is still lots of debate about when these events happen. Thirdly a big volcano can fill the atmosphere with dust particles that reflect back sunlight and reduce the temperature, so it is believed that a massive explosion from Krakatoa caused diminished sunlight and crop failure from AD 535-536 [6]. The lack of clarity round past climate variations and events has two consequences for the global warming debate; it enables frequent re-interpretation of data to retrofit cyclic factors, and it means there is no clear prediction from cyclic solar or orbital effects  that allow refutable predictions.

This brings us to the modern day and the issue of whether the warming we have recently experienced is due to human activities.

Up until recently the observed temperature changes have been around a degree in size. This, as we have seen, is within the limits of much historically observed variation. The hiatus observed since 1998 gave rise to debate as to whether anthropogenic CO2 was the cause particularly given some of the alarmist extrapolations that had been made following the El Nino of 1998 [7]. However the last two years have seen a resurgence of temperature rises taking the observed rise to just over 1.0C from the minima earlier last century. This is at the top end of what was observed in previous warm periods, and even allowing for a temporary spike due to El Nino this rise is going toward new territories.

On top of this the rise in CO2 is marked, although even the amount of CO2 and role is open to some dispute [8 - 10]. Nevertheless, for many scientists the CO2 level is the really scarey bit that is clearly going into new territory rather than the current temperature. The excess CO2 will continue to trap more heat even if we do not add to it.

CO2 and temperature showing the recent large rise in CO2 levels. see also [11]

Its time to make a decision and come down on one side of the argument or other. As someone with a background in physics I find the lack of accuracy and consistency in the data, the lack of experimental evidence that clearly distinguishes between competing views and the poor track record of climate predictions are all frustrating. The basic physics is clear however: CO2 is a known greenhouse gas. There has been a clear increase in atmospheric CO2 to a level not seen since the last ice age. The amount of the increase is about half the total amount emitted by human activity so is consistent with the notion that human activity has caused this increase. The temperature increase is consistent with what would be observed by this increase in CO2, but the relationship is a very broad one. The retained energy is quite small – equivalent to half a days sunlight per year [12], hence the slow growth in temperature we see. 

The two main argument against anthropogenic CO2 are a “not proven” case and a “cyclical climate change” case. The “not proven” case is that the scientific evidence is not strong enough. There is endless querying of measurements, picking out anomalies, and pointing out the failure to predict the next few years in particular the inaccuracy of the more alarmist predictions [7]. Personally I think this case was not without merit until the last couple of years, but the latest uptick in temperatures add to the trend and take it beyond historical limits and into new areas. The balance of probability is that given the unprecedented CO2 levels and the associated greenhouse physics, the long-term trend is in line with what we would expect.

The “cyclical climate change” argument as promoted by people such as Christopher Monckton [13] lacks credibility. There is no clear candidate causative cycle to promote an alternative explanation. Instead we have a quasi-religious argument (see last Climate change post) in that the argument makes no predictions because everything is possible, and any variation of the size we are seeing can be explained after the event as natural variation. Proponents of cyclic variation fail to have any convincing explanation for the massive increase in CO2 levels, and have no explanation why the temperature increase was caused by this cycle and why the increase in CO2 has no effect on global temperatures despite the physics which says it should and has thought the earth's climate history.

I suspect these arguments will not go away. It is quite likely in my opinion that we will see a drop in temperature next year as La Nina replaces El Nino and no real rise over the next ten years [see 14 for measurements of the temperature dropping now from the peak earlier this year], but then there will be another El Nino and another notch up in the temperature. It is possible that the temperature keeps going up from here on and I will cover how that could happen in future posts. What is very unlikely is that the temperature will head back down to the historic average. No-one on the planet has a convincing mechanism that explains how that would happen.

So, with the discussion about man-made global warming having reached a conclusion, I’ll put this to one side and start to look at some of the possible consequences in future posts.

[1] http://www.skepticalscience.com/Bond-Gerard-Bond.html

[2] http://www.skepticalscience.com/loehle-scafetta-60-year-cycle.htm

[3] https://wattsupwiththat.com/reference-pages/solar/

[4] https://www.skepticalscience.com/solar-cycles-global-warming.htm

[5] http://www.climatecentral.org/gallery/graphics/strong-el-nino-brings-warmer-temperatures

[6] https://en.wikipedia.org/wiki/Extreme_weather_events_of_535–536
[7] http://www.theblaze.com/stories/2012/04/23/confession-climate-scientist-says-he-was-extrapolating-too-far-outs-others-as-alarmists-too/
[8] http://benedante.blogspot.co.uk/2015/08/carbon-dioxide-and-end-of-last-ice-age.html
[9] http://www.realclimate.org/index.php/archives/2013/09/paleoclimate-the-end-of-the-holocene/
[10]http://www.co2science.org/articles/V16/N20/EDIT.php
[11] https://wattsupwiththat.com/2012/12/07/a-brief-history-of-atmospheric-carbon-dioxide-record-breaking/
[12] http://www.climate-lab-book.ac.uk/2016/slowdown-discussion/#more-4375

[13] http://www.lordmoncktonfoundation.com

[14] https://wattsupwiththat.com/2016/08/16/july-2016-global-surface-landocean-and-lower-troposphere-temperature-anomaly-update/

Canvey Again

Canvey Wick again, and a much more successful visit than last time.

First up was a Brown-Banded Carder Bee (Bombus Humilis). Quite difficult to photograph in the breeze but I think you can make out on both photos the single brown band that runs across near the top of the abdomen. Otherwise a generally pale buff bee.

Then a number of Shrill Carder Bees (Bombus Sylvarum). These were quite small and showed a distinctive colour sequence: black band on the thorax between two white stripes, then a clear black band on the abdomen above a small but distinctive orange tail. Compare the photo below with this, clearly the same bee! Thrilled to encounter these two splendid bees.

Otherwise a Clouded Yellow flew strongly down the bee path, and there were plenty of Common Blues, and various commoner butterflies. 

finally a plump dark Adder slithered quickly off the path, no doubt disturbed by my heavy footfall. 

So, a fantastic selection of wildlife in a small yet spectacular reserve.

Climate Change Interlude - On Science.

We are about to look at the various theories and opinions that proliferate in the debate on the origins of recent global warming. It is very easy to get lost in this. You read one article and think –yes, that looks convincing. Then you read an article saying the opposite and think – well yes they make some good points too. So what are we to think?

The debate is a scientific one, so first we should define what we mean by science. What is a scientific theory? how is a scientific theory evaluated?

To start with the fount of all modern knowledge, Wikipedia [1], “A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed, preferably using a written, pre-defined, protocol of observations and experiments.” Furthermore, “Scientific theories are usually testable and make falsifiable predictions”, and “Scientists use theories as a foundation to gain further scientific knowledge, as well as to accomplish goals such as inventing technology or curing disease.”

There are a couple of distinct strands here. Firstly, a theory must agree with lots of evidence acquired through experimentation, and it must make testable and falsifiable predictions. This is the classical definition most of us recognise from our school or university days. But there is a second element that we can use the theory to do or make something. In short, a theory should be useful. Note that it doesn’t have to be “correct” or “true”. It just has to explain enough of what we see consistently enough, and we have to be able to make predictions that are sufficiently reliable for us to be able to control the environment around us with confidence.

It is worth looking at another debate to help illuminate our thoughts on scientific theories. The validity of the Theory of Evolution is still debated in some parts of the world with Creationism being a preferred alternative. In the definition of a theory as given above the objection to Creationism is clear. It isn’t that Creationism is “wrong” – after all, if there is a higher all-powerful being that creates everything we see according to their higher plan, then who are we to refute that. The objection is that Creationism is not a scientific theory. It doesn’t allow or support enquiry on why we see the things we see; the things we discover are here because God put them here. It doesn’t allow us to speculate about the future; who are we to debate God’s plans for the world and its inhabitants? There are no experiments that can be performed, no predictions that can be tested. Ultimately the problem with Creationism is that it doesn't meet the criteria for a scientific theory. It is a religious theory, not a scientific one.

Computer models, fitting data, and estimation.

Science is very good at understanding systems of a single variable or a couple, but once you get a number of variables that are mutually dependent, things get very hard. Typically work progresses by fitting data to historic data and then using the best-fit parameters to extrapolate into the future. One of the things to watch out for is “over-fitting” which is that the more parameters you add the better the fit to historical data but often the fit to future data gets worse as your parameters are fitting to random elements of your data set. Parsimonious models with few parameters and simple relationships are generally preferred. If you try to extrapolate what happens into an area not covered by your data set (e.g. high CO2 levels) then your models may no longer work as new and un-predicted 

Another point about models is that fitting models to continuous distributions is problematic enough but fitting to distributions of binary events is horrendous; you need enormous amounts of data before you can make any solid statements. For instance, if your theory predicts changes in events of the order of a small number per century, you need several centuries of data before you can begin to get any certainty you are correct.

And so to climate change. There are two main problems that appear when we apply the expectations of scientific theories to climate.

Firstly, while the physics may be simple, the way the climate responds is very complicated; there are lots of variables, they differ for many parts of the world, and they are inter-dependent. Inevitably scientists end up fitting models to historic data. Scientists have become adept at developing theories that explain historical phenomena (see a previous post about the Hiatus), they are less good at predicting what is going to happen in the near-future both for the reasons given above and because we are going from a period of known climate into a future where some key variables have changed, and some other relationships may change in nature.

Secondly, we cannot easily test theories. We don’t have a spare earth we can treat differently. We have to take what nature has provided and try and draw scientific conclusions from that. This means that the proven ability of scientific climate theories to predict is much lower than for many areas of physics, for instance. Climate science is bit like doing particle physics but without a collider, instead restricted to observing particle interactions that take place naturally.

In summary, we are engaged in the business of science. We need to see theories explaining past measurements and predicting future ones. Experimentation is difficult – we need to take what nature has given us with no scope for independent assessment. Finally, theories that predict extreme events requires loads of data to have any scientific validity which may take us beyond the timescale required for action.

Next, a look at the Holocene; from the last ice-age to the present day.

[1] https://en.wikipedia.org/wiki/Scientific_theory

Could Recent Warming be Due to Natural Variation in the earth's climate? Part 2 Ice ages and Solar Cycles

We start where the last post ended, the closure of the Panama gap around 2 million years ago which led to a loss in transport of warm water to the north pole. Erosion of the newly-formed mountain ranges such as the Himalayas slowly reduced the CO2 in the atmosphere and the earth slowly grew colder with ice building at the poles [1]

The causes of ice ages are not completely understood [2]. A strong theory is that slight changes in solar radiation being received due to orbital changes can then amplified through a number of positive feedback processes. The reflection of sunlight back from ice and snow reduces the net heating of the sun, and the formation of large ice sheet reduces the flows of oceans to and from the ice sheets leading to further increase in ice formation. Analysis of trapped air bubbles shows that greenhouse gases drop by a third (CO2) and a half (methane) during glaciation. There is some dispute on whether CO2 levels lead or lag the temperature changes[3], though there seems to be some consensus that in ice ages it lags – the forcing is the solar radiation which drives temperature, and the amount of CO2 in the atmosphere follows the change in temperature.

Building an ice age can take 80,000 years, but getting rid of ice can occur much faster – only 4,000 years. There are a number of reasons for this speed of deglaciation but the major reason would seem to be the rise in sea levels undercutting the ice sheet and causing more melting leading to a rapid melting of the ice sheet. During this deglaciation the water level increases massively – lowest to current is about 120m [4], so at some point the Mediterranean was a lake, then a salt basin, then flooded again.

The frequency of ice ages has been much analysed. They are clearly periodic but not so regular as to make explanation easy. The most obvious source of a periodic forcing variable is oscillations either in the earth’s orbit round the sun or from the sun itself. There are three separate cycles that interact: changes in eccentricity (the ratio of the length of the earth’s orbit to the width, the orbit being an ellipse not a circle); changes in the tilt of the earth’s axis of rotation, and precession of the tilt. These periodic oscillations known collectively as Milankovitch cycles interact to make ice ages more or less likely. The periods of oscillation of these aspects of the earth’s rotation are 96,000 years, 41,000 years and 27,000 years respectively. The combined effects are sufficiently vague in frequency and amplitude to be capable of continued re-interpretation [5]. Furthermore if all else fails then meteors or super-volcanoes can always be invoked to explain a sudden cooling [6]

I’ve attached a chart that illustrates the temperature and CO2 [7]. We are in the thick blue blob on the RHS. Possibly the most interesting part of the chart is the massive increase in CO2 on the RHS to a level not seen for the duration of this chart (400,000 years) which I'll return to shortly.

As we approach the Holocene (the name given to our current inter-glacial period starting nearly 12,000 years ago) we get a feel for the way temperature climate changes work – a forcing variable, then positive feedback mechanisms such as changes in ice and CO2 that drive the change until it reaches a new equilibrium. Then a switch back in the forcing variable until a new equilibrium is reached.

Next we consider the Holocene and look at the various explanations for the warming we are currently experiencing, but first I’ll put in a small post on the nature of science to give us some tools to tackle the debates that are going on about the warming we have seen recently.

[1] https://www.newscientist.com/article/dn18949-the-history-of-ice-on-earth/

[2] http://www.bbc.co.uk/science/earth/water_and_ice/ice_age

[3] http://www.scientificamerican.com/article/what-thawed-the-last-ice-age/

[4] https://en.wikipedia.org/wiki/Past_sea_level

[5] http://www.skepticalscience.com/Milankovitch.html

[6] https://en.wikipedia.org/wiki/Ice_age#Causes_of_ice_ages

[7] https://wattsupwiththat.com/2012/04/11/does-co2-correlate-with-temperature-history-a-look-at-multiple-timescales-in-the-context-of-the-shakun-et-al-paper/

Could Recent Warming be Due to Natural Variation in the earth's climate? Part I A (very brief) history of the earth's climate

One explanation of recent global warming is natural variation in climate. The world has been warmer, colder, wetter, drier, and that what we are seeing is just part of that historic variation. So I’ve read a small book [1] and here goes …

According to the book “The climate system is very straightforward”. The key facts are that the equator gets much more heat from the sun per square meter than the poles, that the earth is spinning, and that the earth’s axis is at a small angle and rotates with respect to the sun giving us an annual cycle of seasons. Heat energy goes from the equator to the poles via the atmosphere and oceans to (partially) redress the differential in radiative energy. This has been the case since the creation of the earth, but climate has varied considerably over this time, and the main factor in driving this large scale change in climate has been the location of land mass on the earth’s surface. This determines how the oceans flow and distribute heat and has been the principal determinant in the earth’s climate history.

The current view is that there was a single supercontinent “Rodinia” formed 1100 million years ago, which broke up and reassembled to form “Pangea” about 300 million years ago. This started to fragment about 200 million years ago. About 100 million years ago Antarctica moved into position, but at this stage was warm and populated by dinosaurs. Finally about 50 million years ago the continents were in positions we recognise as being substantially the same as today.

The current position of the continents is the key determining factor in creating our polar-based energetic climate. When oceans had clear access to the poles ice forming at the poles was blown away from the poles and melted in the warmer latitudes, so polar regions remained temperate. About 2 million years ago a critical event happened. South America and North America joined at Panama. The closure of this gap cut off a key ocean flow from the equatorial regions to the poles. this reduced the ability to transport warmth to the heat-starved poles and brought in the period of the great ice-ages. The surrounding ocean takes heat away, so ice collects on the land-mass and adjacent ice shelves, and there is a temperature difference of 60C between equator and pole. In the northern hemisphere the pole is ocean but the surrounding ring of continents limits the movement south of ice and enables the ice to build up and a temperature difference of 40C results.[2]

When the continents first moved into the current configuration the world was a warmer place with much more carbon dioxide in the atmosphere. This period saw the creation of major mountain ranges, and it is believed that weathering of the mountains took carbon dioxide out of the atmosphere specifically through the reaction of carbonic acid in rain with silicates to form insoluble carbonates. This reduction in CO2 lead to cooling and a more familiar temperate climate. Overall CO2 levels have varied greatly over time but have “recently” decreased to historic lows – see the chart below.[3]

So, it's been hotter, colder, with much more CO2 but never less CO2. There are broad-brush explanations for most of this large-scale variation.

The next time-scale we need to look at is the more recent one of ice-ages, and I'll look at that next.

[1] “Climate. A very short Introduction” by Mark Maslin (Oxford)

[2] https://wattsupwiththat.com/2015/02/13/north-and-south-poles-important-climate-differences/

[3] http://www.pnas.org/content/99/7/4167.full