Our Changing Climate: A Guide for HKDSE Geography
Hello! Welcome to your study notes for the "Climate Change" chapter. Don't worry if this topic seems big and complicated. We're going to break it down into simple, easy-to-understand parts. We'll explore what climate change is, why it's happening, and how it affects us right here in Hong Kong and across the world. Understanding this is super important because it's about the future of our planet! Let's get started.
Part 1: The Basics - Weather vs. Climate
What's the difference?
People often mix up these two terms, but they are quite different. It's a common mistake, so let's clear it up!
Weather is what's happening in the atmosphere right now or over a very short time. Is it sunny today? Is a typhoon coming tomorrow? That's the weather.
Climate is the average weather pattern in a place over a long period, usually 30 years or more. Hong Kong's climate is subtropical, which means we expect hot, humid summers and mild, dry winters.
Analogy Time! Think of it like this: Weather is your mood today (happy, sad, angry), while Climate is your overall personality (cheerful, serious, calm). Your mood can change every day, but your personality stays pretty consistent.
Climate on Different Scales
We can talk about climate on three main levels:
Local scale: The climate of a small area, like Hong Kong.
National scale: The climate of an entire country, like China.
Global scale: The climate of the entire planet Earth.
Key Takeaway
Weather is short-term and changes daily. Climate is the long-term average pattern. Global warming is about a change in the global climate, not just a few hot weather days.
Part 2: The Earth's Report Card - Evidence for Climate Change
How do we know the climate is actually changing? Scientists have collected a lot of evidence. It's like a doctor checking a patient's symptoms. Here are the key signs that our planet is warming up.
1. Sharp increase in global temperature: Global average temperatures have been rising rapidly, especially in the last few decades. The planet is running a fever!
2. More frequent heat waves: We're seeing more periods of unusually hot weather around the world.
3. Melting glaciers and ice sheets: Huge bodies of ice in places like the Arctic and Antarctica are melting at an alarming rate.
4. Sea-level rise: When glaciers melt, the water flows into the ocean. Also, as water gets warmer, it expands. Both of these cause the sea level to go up, which threatens coastal areas with flooding.
5. More frequent extreme weather events: Scientists have observed an increase in the intensity and frequency of events like super typhoons, heavy rainfall (leading to floods), and long periods without rain (droughts).
Did you know?
The speed at which sea levels are rising has more than doubled from the 20th century to today. This puts coastal cities, including parts of Hong Kong, at greater risk of flooding in the future.
Part 3: The Big Question - Why Is It Getting Warmer?
To understand global warming, we first need to know about something called the Greenhouse Effect. It's not a bad thing on its own—in fact, we need it to live!
The Greenhouse Effect: Earth's Natural Blanket
Think of the Earth having a natural, invisible blanket made of gases called greenhouse gases (like Carbon Dioxide). Here's how it works:
Step 1: Energy from the sun (shortwave radiation) travels through the atmosphere and warms the Earth's surface.
Step 2: The warmed Earth sends heat back out towards space (longwave radiation).
Step 3: The "greenhouse gas blanket" traps some of this outgoing heat, keeping our planet at a warm and stable temperature (around 15°C on average) suitable for life.
Without this natural effect, the Earth would be a frozen, lifeless planet!
The Enhanced Greenhouse Effect: Too Many Blankets!
The problem starts when we make the blanket thicker by adding more greenhouse gases to the atmosphere. This is the enhanced greenhouse effect. A thicker blanket traps too much heat, causing the Earth's temperature to rise. This is what we call global warming.
Human activities are the main reason for this "thicker blanket."
Human Activities Causing Global Warming
1. Burning Fossil Fuels: When we burn coal, oil, and natural gas for electricity, factories, and transport (cars, buses, planes), we release huge amounts of Carbon Dioxide (CO₂), the main greenhouse gas.
2. Deforestation: Forests are like the Earth's lungs. Trees absorb CO₂. When we cut down or burn forests, we not only stop them from absorbing CO₂, but we also release all the carbon stored in them back into the atmosphere.
3. Agriculture: Farm animals, especially cows, release large amounts of Methane (CH₄), another powerful greenhouse gas, when they digest food. Also, certain farming practices release other greenhouse gases.
4. Garbage Burning and Landfills: When organic waste in landfills rots without oxygen, it produces methane. Burning garbage also releases CO₂.
5. Emission of Chlorofluorocarbons (CFCs): These were used in old refrigerators, air conditioners, and spray cans. They are extremely powerful at trapping heat. While they are now banned, they stay in the atmosphere for a very long time.
Natural vs. Human Causes
The Earth's climate does change naturally over thousands of years due to things like volcanic eruptions and cycles in the sun's energy. However, the warming we've seen in the last century is happening much, much faster than any natural cycle. The vast majority of scientists agree that this rapid warming is caused by the greenhouse gases released from human activities.
Quick Review
The natural greenhouse effect is essential for life. The enhanced greenhouse effect, caused by human activities adding extra greenhouse gases, is causing global warming.
Part 4: Climate Change in Our Backyard - The Urban Heat Island Effect
Have you ever noticed that it feels much hotter in busy urban areas like Mong Kok or Central compared to the New Territories countryside? This is a real phenomenon called the Urban Heat Island (UHI) Effect. It's a perfect example of how human development changes the local climate (or microclimate).
Why are cities hotter?
Dark Surfaces: Concrete buildings and dark asphalt roads absorb and store more of the sun's heat compared to grass and trees, which reflect it.
Building Geometry: Tall buildings create "urban canyons" that trap heat and block cooling winds.
Less Vegetation: Fewer trees and parks mean less cooling from shade and a process called evapotranspiration (where plants release water vapour, cooling the air).
Waste Heat: Cars, buses, factories, and air conditioners all pump out heat, adding to the warmth of the city.
These factors can make a city several degrees Celsius warmer than its surrounding rural areas, especially at night. This is very noticeable in a dense city like Hong Kong. The UHI effect also changes other parts of the city's climate, like wind patterns and sometimes even rainfall.
Part 5: Consequences of Climate Change - How It Affects Us All
Climate change isn't just about the planet getting a bit warmer. It has serious consequences for the environment and for people. The syllabus talks about "winners and losers," meaning some effects might be slightly beneficial for a few, but they are overwhelmingly negative for most.
Key Impacts:
Impact on Sea Level & Flooding: As mentioned, rising sea levels will lead to more frequent and severe coastal flooding. This is a huge threat to low-lying coastal areas and cities, like the Netherlands, Bangladesh, and even parts of Hong Kong.
Extreme Weather Events: Expect more powerful typhoons, heavier rainstorms, and more intense heat waves. This can cause damage to homes, infrastructure, and agriculture.
Health Risks: Higher temperatures and more frequent heat waves can lead to heatstroke and other health problems. Warmer climates can also allow diseases carried by insects like mosquitoes to spread to new areas.
Changes to Farming: Some areas may become too hot or dry to grow crops, leading to food shortages (these are the "losers"). However, a very small number of colder regions, like parts of Siberia or Canada, might become warm enough to start farming new crops (these could be the "winners").
Unpredictable Climate: As the climate changes, it becomes harder for us to predict weather patterns, which makes planning for farming, water supply, and disaster prevention much more difficult.
Part 6: What Can We Do? Taking Action
So, what's the solution? There are two main approaches: mitigation and adaptation.
Mitigation: Tackling the Cause
Mitigation means reducing the amount of greenhouse gases we release to slow down or stop climate change. It's about fixing the root of the problem.
Examples:
- Switching from fossil fuels to renewable energy (solar, wind).
- Improving energy efficiency (using less electricity).
- Protecting forests and planting new trees (afforestation).
- Using public transport, walking, or cycling instead of driving.
Adaptation: Coping with the Effects
Adaptation means making changes to our lives and society to cope with the effects of climate change that are already happening or are unavoidable.
Examples:
- Building sea walls and flood defences to protect coastal areas.
- Developing new crop types that can survive in hotter or drier conditions.
- Creating better warning systems for extreme weather events like typhoons and heat waves.
- Creating more green spaces in cities to help reduce the Urban Heat Island effect.
Why is a Global Agreement So Difficult?
Tackling climate change requires the whole world to work together, but this is very complex.
Conflicting Views: Developed countries (like the USA and Europe) became rich by burning fossil fuels for over a century. Now, developing countries (like China and India) say they need to burn fossil fuels to grow their economies and lift their people out of poverty. They argue it's unfair for rich countries to demand they stop.
Economic Costs: Shifting to a green economy costs a lot of money, and there are debates about who should pay for it.
These conflicting interests make it very difficult for all countries to agree on and stick to a global plan.
Chapter Summary: Key Takeaways
Let's do a final, quick review of the most important points!
1. Climate vs. Weather: Climate is the long-term average (personality), while weather is the short-term condition (mood). Climate change is a shift in the long-term pattern.
2. The Greenhouse Effect: It's a natural process that keeps Earth warm. The enhanced greenhouse effect is caused by human activities adding extra gases, which traps too much heat and causes global warming.
3. Key Causes: The main human activities causing global warming are burning fossil fuels, deforestation, and agriculture.
4. Local Impact - UHI: Cities like Hong Kong create their own "Urban Heat Islands," making them hotter than surrounding rural areas due to human structures and activities.
5. Consequences & Solutions: The impacts are serious (sea-level rise, extreme weather). We can respond with mitigation (tackling the cause) and adaptation (coping with the effects). Reaching a global agreement is difficult due to conflicting interests.