Can my IB ESS IA be about climate change?

Yes, but it needs to become local, measurable, and grounded in primary data for IB ESS. Climate change works best when it is used as context rather than the entire investigation. For example, you might investigate an urban heat island effect by measuring temperature differences across land-use types, then discuss climate resilience. You can also look at carbon-related choices (transport habits, energy use) if your data collection is structured and you evaluate uncertainty honestly. The key is avoiding “global trends” you cannot test yourself. A good rule is: if the only way to answer it is to cite big datasets, it is not yet an IA-ready IB ESS question.

Do I need primary data, or can I use secondary sources?

You need primary data at the core of an IB ESS IA, even if secondary sources help you interpret results. Secondary data is great for background context, comparing your findings to published research, or justifying site choice. But marks come from how you design and carry out your investigation, how you process and treat your data, and how you evaluate limitations. If you are mainly summarizing reports from other organizations, you drift into being descriptive. A strong approach is “primary data first, secondary data to deepen evaluation.” That balance usually produces more analysis and stronger conclusions in IB ESS.

Should I choose a complex topic to impress examiners?

Most top-scoring IB ESS IAs are simple in design and strong in reasoning. Complexity often adds noise: inconsistent methods, missing trials, or data you cannot explain. Examiners are not awarding marks for fancy equipment or obscure chemistry; they award marks for clarity, reliability, analysis, and evaluation. A simple study with careful repeats, clear variables, and thoughtful uncertainty can outperform a complicated design with shaky execution. If you want to “impress,” do it with sharp evaluation and systems thinking. In other words, make your thinking complex, not your method.