CCS Week 1 - Introduction To Cimate Change

The Earth’s climate has changed drastically over its lifetime. Science has described and proposed explanations of these changes. Until very recently, these changes have progressed slowly, taking thousands or millions of years between stable periods. Accelerating changes in various climate indicators (average sea and land temperatures, ice coverage etc) characterise the past 100 years, far exceeding observations and analysis of past changes. The changes happen in concert with humanity’s advancing industrialisation. Scientific concensus determines a causal link between these two things: human changes affect global climate.

1.1 Key principles of climate change

The course introductory video establishes a baseline explanation for the process of global warming. It describes a “blanket effect”: certain atmospheric gasses allow shorter-wave heat energy from the sun to reach the Earth’s surface. The surface (made up of sea, ice, land, vegetation and so on) absorbes some of this energy but also reflects some back, at longer wavelengths. These reflected energy is mostly absorbed by the same atmospheric gasses, but then re-emitted back towards the surface, helping raise tempteratures at the surface. This process has developed over time to create the conditions we are famililar with, but over the past 100 years human activities have raised the levels of these gasses in the atmosphere, so that more energy is redirected towards the surface. This causes temperatures to rise and climate to change.

Historically, scientists called this the “greenhouse effect”, and the gasses “greenhouse gasses”. Broadcast and print media have popularised this term over the past few decades. However, some now think “the blanket effect” better describes the process. Greenhouses primary function is to prevent convection of heat energy upwards by reducing air flow. A blanket, in contrast, traps heat between its source and the material of the blanket.

We were asked a couple of questions. My answers follow:

1. Has your understanding of the greenhouse effect changed? My understanding of the greenhouse effect has changed a little. I understand now that a greenhouse’s retained heat owes more to reduced internal convection — due to lower air flow, resulting in bodies in the space retaining more heat — than to heat radiation being reflected inward by the glass. I understand the greenhouse analogy has flaws: the greenhouse keeps heat mostly due to convection, but Earth does not have this reduced convection. I learned the Earth would be cooler without these gasses. I learned that H₂O and N₂O are significant “greenhouse” gasses (I knew about CO₂ and CH₄ before). The video introduced me to the “blanket effect” analogy for the first time. I can see why the analogy gets made.

2. Should we adopt ‘the blanket effect’ as an analogy instead of ‘the greenhouse effect’? Within the course and science, I’m ambivalent whether “greenhouse” or “blanket” is used. The impact of albedo, the mixed action of the gasses (trapping, re-emitting heat) all make the situation much more complex than the simple analogies. I’m content to use “blanket”… But outside science, in mass media, in coffee-shop conversations and such-like, the “greenhouse effect” carries all the weight, but also sounds less worry-some than the current scientific messaging suggests.

1.3 Blanket Earth

NASA makes significant contribution to climate science. Most practially, they have placed into orbit much of the equipment used to monitor Earth’s atmosphere. Their scientists use their knowledge to assess climate here and on other planets. The publicaly publish a lot of their work, and produce educational material to support the wider community.

Insulating gasses

This NASA article, linked by the course, explains the effect on climate of certain atmospheric gasses. It goes on to give examples of the effects on other planets and provides insight into how humanity’s recent activities are affecting the system.

The article mentions five gasses (or families of gasses), and describes their effects. It groups them into two categories:

1. Feedbacks produce short-term effects on climate with a tendancy in one direction, but also a counter-effect under certain circumstances. Water vapour has a positive feedback cycle: light from the sun generates heat at the surface, producing water vapour, which acts as an insulator, futrther increasing surface temperaturs, leading to more evaporating water. The counter effect arrises when water vapour condenses to clouds: the clouds reflect sunlight before the energy can reach the EArther’s surface, providing a cooling or balancing effect.

2. Forcings produce longer term effects, firmly in one directon. Science has gathered strong evidence that human activities lead to increases in concentrations of thesee gasses and hence increases in the effect the produce. Methane has a powerful insulating effect, reflecting heat back to the planet’s surface and promoting temperature increases. Methane production has risen due to agriculture and livestock farming, and decomposing landfill waste.

Naturally occuring greenhouse or blanket effects on Earth gave rise, over time, to the conditions that allow life as we know it to flourish. On Mars the effect appears greatly reduced, oweing to much lower quantities of atmospheric gasses. Venus’ very high concentration of carbon dioxide leads to surface temperatures which can melt lead.

Climate changes

The increasing blanket effect seems produce a number of effects:

• raised surface temperatures
• raised overall water evaporation
• higher sea temperatures and reduce ice formation
• the reduced ice formation will futher raise temperatures due to the resulting reduction in overal planet albedo
• vegetation changes as plants respond to new conditions

Human input

Human activities such as population expansion and industrialisation of farming, equipement production, motor transport and increased urban living have raised the amount of CO₂, H₂O, CH₄ and N₂O emissions.

Solar irradiance

Light from the sun provides the energy for most systems at the Earth’s surface, particularly the ones living organisms rely on. A common argument agasint human-driven climate change proposes that observed changes in climate happen as a result of changes in radiation from the sun. The argument has a reasoned basis: energy from the sun is produced in chemical and nuclear reactions in the sun’s core, which fluctuate over time; these fluctuation lead to differeing solar surface conditions and varying radiation emmisions. However, records show the energy from the sun has changed very little, even dropping in very recent times. This strongly suggests the global warming effects do not arise from changes in solar irradiation of the Earth.

1.5 What is climate?

The course material for this section centerd on a video discussing the differences between climate and weather.

• Weather refers to the atmospheric phenomena experienced day to day or week by week. These include rainfall, air temperature, wind, snow and so on.
• Climate refers to the totals and averages of those phenomena over much longer periods, and paying attention to their changes from year to year. The video claims scientists consider averages over 30 years as strong climate indicators.

I suppose the processes which drive these phenomena: seasonal solar irradation, air currents, the water cycle and their interations all contribute to the analysis of both clinmate and weather.

In day-to-day conversation, many people use climate and weather interchangably. Comments in the discussion thread suggested some languages have only one word for these phenomena. Growing up in the UK and having travelled to many countries, for short trips, I had come to understand climate as the yearly cycles of weather changes. Whilst I knew scientists and would be paying attention to changes in these patterns over time, I had not appreciated they made such a long-term distinction between the two.

1.8 What factors affect climate change

The primary resource for this section comes from the Intergovernmental Panel on Climate Change (IPCC). Their summary poster shows statistics and projections for global “greenhouse” gas concentrations, surface temperature, water temperature and Artic and Antarctic ice extents. These criteria describe the salient features Earth climate macrocosm, both forces acting on the climate and also measureable effects, or “symptoms” of the changes.