evsc week 7 - climate change and PB

Describe changes in fossil-fuel carbon emissions from 1959 to 2014. 

rose sharply - more than quadrupling due to industrial growth and increased energy use, leading to higher atmospheric CO₂ and global warming.

• squiggle up and down due to trees/seasons/carbon release

Describe changes in the uptake of carbon by the atmosphere, oceans, and terrestrial biosphere from 1959 to now. 

significant increase in the absolute amount of CO2 absorbed by all reservoirs, driven by the sharp rise in human emissions.

• the proportion of emissions being absorbed has remained relatively stable, while the atmosphere's share has grown significantly.

Explain why atmospheric CO2 concentrations changed over the past 50 to 60 years.

due to human activities that have overwhelmed Earth's natural carbon cycle.

what is one of the main drivers of CO2 concentrations changes?

The continuous and accelerating combustion of fossil fuels

• Secondary sources include deforestation and land-use change.

what absorbs CO2 emissions

The oceans and terrestrial biosphere absorb about half of these human emissions; the other half remains in the air, causing the CO2 concentration to rise year after year.

Describe how greenhouse gases affect Earth's surface temperatures. 

absorb and re-emit infrared radiation that is reflected from the surface, trapping heat and thereby increasing the planet's average surface temperature.

natural greenhouse effect

atmospheric gases like H2O and CO2 trap heat, keeping Earth's average temperature at a life-sustaining +15 degrees Celsius.

human greenhouse effect

The harmful amplification of this natural blanketing, primarily caused by human emissions from burning fossil fuels, adds excess greenhouse gases and causes the planet to warm rapidly above its natural balance.

Identify the planetary boundary for climate change.

The planetary boundaries are 350 ppm CO₂ and +1.0 W/m² of radiative forcing.

current state of the planetary boundary (radiative forcing)

The current energy imbalance is > 2.3 watts per square meter.

• The zone of uncertainty for this control variable is 1.0 - 1.5 watts per square meter.

control variable for climate change

atmospheric CO₂ concentration and energy imbalance (radiative forcing).

• The control variable is defined as the Energy Imbalance: The energy imbalance in terms of radiative forcing measured at the top of the atmosphere.

Evidence shows that recent global warming is caused by human activities because:

• Rising CO₂ levels match the timing of increased fossil-fuel burning since the industrial revolution.

• Climate models show that natural factors alone (like solar changes or volcanic activity) cannot explain the observed warming.

• Atmospheric measurements confirm that CO₂ from fossil fuels accumulates in the atmosphere.

this evidence debunks common myths:

• “The Earth is just warming naturally” → Natural factors can’t account for the rapid rise in temperature.

• “CO₂ isn’t increasing” → Atmospheric CO₂ is at record highs, far above pre-industrial levels.

• “Weather fluctuations disprove climate change” → Short-term weather changes don’t negate long-term trends.

what is the first piece of evidence for changing climate

Atmospheric CO2 Concentration: The concentration is significantly above the planetary boundary < or equal 350 ppm.

what is the second piece of evidence for changing climate

Energy Imbalance (Radiative Forcing): The current state is significantly greater than the planetary boundary of +1.0 W/m².

• This excess energy trapped by the enhanced greenhouse effect provides the physical evidence that the Earth system is accumulating heat, directly resulting in global warming

actions that we need to take to reduce future global warming.

1. Drastically cut greenhouse gas emissions, especially from fossil fuels

2. Transition to renewable energy sources like solar and wind

3. Increase energy efficiency in industry, transport, and buildings

4. Protect and restore forests and other carbon sinks

5. Adopt policies and technologies that limit radiative forcing and stay within carbon budgets

basic science behind the planetary boundary

Climate change occurs when Earth’s energy budget is altered—mainly because humans burn fossil fuels, adding greenhouse gases (GHGs) to the atmosphere. GHGs absorb and re-emit longwave (infrared) radiation emitted by Earth (Stefan-Boltzmann law), trapping extra heat and creating a human-enhanced greenhouse effect.

radiative forcing

describes the amount of excess energy trapped within the Earth’s climate system due to the variation of a climate change factor such as GHG concentrations.